Airflow control in active cooling systems

ABSTRACT

A system including at least one heat-generating structure and a cooling system is described. The cooling system includes a cooling element and an exhaust system. The cooling element is in communication with a fluid and is configured to direct the fluid toward the heat-generating structure(s) using vibrational motion. The exhaust system is configured to direct fluid away from the heat-generating structure to extract the heat and/or to draw the fluid toward the cooling element.

CROSS REFERENCE TO OTHER APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 62/949,383 entitled AIRFLOW CONTROL SYSTEM IN PIEZOELECTRIC COOLING FOR DEVICES filed Dec. 17, 2019 which is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

As computing devices grow in speed and computing power, the heat generated by the computing devices also increases. Various mechanisms have been proposed to address the generation of heat. Active devices, such as fans, may be used to drive air through large computing devise, such as laptop computers or desktop computers. Passive cooling devices, such as heat spreaders, may be used in smaller, mobile computing devices, such as smartphones, virtual reality devices and tablet computers. However, such active and passive devices may be unable to adequately cool both mobile devices such as smartphones and larger devices such as laptops and desktop computers. Consequently, additional cooling solutions for computing devices are desired.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings.

FIGS. 1A-1E depict an embodiment of an active cooling system including a centrally anchored cooling element.

FIGS. 2A-2B depict embodiments of cooling elements usable in active cooling systems including centrally anchored cooling elements.

FIGS. 3A-3B depict embodiments of cooling elements usable in active cooling systems including centrally anchored cooling elements.

FIGS. 4A-4C are diagrams depicting an embodiment of an active cooling system.

FIGS. 5A-5E depict an embodiment of an active cooling system formed in a tile.

FIGS. 6A-6C depict embodiments of an active cooling system including an exhaust system used in a closed device.

FIGS. 7A-7C depict embodiments of an active cooling system including an exhaust system used in an open device.

FIG. 8 is a plan view of an embodiment of an active cooling system usable with a heat-generating structure.

FIGS. 9A-9B are diagrams of a portion of an embodiment of an active cooling system usable with a heat-generating structure.

FIG. 10 is a diagram depicting a side view of a portion of an embodiment of an active cooling system usable with a heat-generating structure.

FIG. 11 is a diagram depicting a side view of a portion of an embodiment of an active cooling system usable with a heat-generating structure.

FIGS. 12A-12B are diagrams of a portion of an embodiment of an active cooling system usable with a heat-generating structure.

FIGS. 13A-13B are diagrams of a portion of an embodiment of an active cooling system usable with a heat-generating structure.

FIG. 14 is a diagram depicting a side view of a portion of an embodiment of an active cooling system usable with a heat-generating structure.

FIG. 15 is a diagram depicting a side view of a portion of an embodiment of an active cooling system usable with a heat-generating structure.

FIG. 16 is a diagram depicting a side view of a portion of an embodiment of an active cooling system usable with a heat-generating structure.

FIG. 17 is a diagram depicting a side view of a portion of an embodiment of an active cooling system usable with a heat-generating structure.

FIG. 18 is a flow chart depicting an exemplary embodiment of a method for operating a cooling system.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as a process; an apparatus; a system; a composition of matter; a computer program product embodied on a computer readable storage medium; and/or a processor, such as a processor configured to execute instructions stored on and/or provided by a memory coupled to the processor. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention. Unless stated otherwise, a component such as a processor or a memory described as being configured to perform a task may be implemented as a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. As used herein, the term ‘processor’ refers to one or more devices, circuits, and/or processing cores configured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.

As semiconductor devices become increasingly powerful, the heat generated during operations also grows. For example, processors for mobile devices such as smartphones, tablet computers, notebooks, and virtual reality devices can operate at high clock speeds, but produce a significant amount of heat. Because of the quantity of heat produced, processors may run at full speed only for a relatively short period of time. After this time expires, throttling (e.g. slowing of the processor's clock speed) occurs. Although throttling can reduce heat generation, it also adversely affects processor speed and, therefore, the performance of devices using the processors. As technology moves to 5G and beyond, this issue is expected to be exacerbated.

Larger devices, such as laptop or desktop computers include electric fans that have rotating blades. The fan that can be energized in response to an increase in temperature of internal components. The fans drive air through the larger devices to cool internal components. However, such fans are typically too large for mobile devices such as smartphones or for thinner devices such as tablet computers. Fans also may have limited efficacy because of the boundary layer of air existing at the surface of the components, provide a limited airspeed for air flow across the hot surface desired to be cooled and may generate an excessive amount of noise. Passive cooling solutions may include components such as a heat spreader and a heat pipe or vapor chamber to transfer heat to a heat exchanger. Although a heat spreader somewhat mitigates the temperature increase at hot spots, the amount of heat produced in current and future devices may not be adequately addressed. Similarly, a heat pipe or vapor chamber may provide an insufficient amount of heat transfer to remove excessive heat generated.

Varying configurations of computing devices further complicate heat management. For example, computing devices such as laptops are frequently open to the external environment while other computing devices, such as smartphones, are generally closed to the external environment. Thus, active heat management solutions for open devices, such as fans, may be inappropriate for closed devices. A fan driving heated fluid from the inside of the computing device to the outside environment may be too large for closed computing devices such as smartphones and may provide limited fluid flow. In addition, the closed computing device has no outlet for the heated fluid even if the fan can be incorporated into the closed computing device. Thus, the thermal management provided by such an open-device mechanism may have limited efficacy. Even for open computing devices, the location of the inlet and/or outlet may be configured differently for different devices. For example, an outlet for fan-driven fluid flow in a laptop may be desired to be located away from the user's hands or other structures that may lie within the outflow of heated fluid. Such a configuration not only prevents the user's discomfort but also allows the fan to provide the desired cooling. Another mobile device having a different configuration may require the inlets and/or outlets to be configured differently, may reduce the efficacy of such heat management systems and may prevent the use of such heat management systems. Thus, mechanisms for improving cooling in computing devices are desired.

A system including at least one heat-generating structure and a cooling system is described. The cooling system includes a cooling element and an exhaust system. The cooling element is in communication with a fluid and is configured to direct the fluid toward the heat generating structure(s) using vibrational motion. The exhaust system is configured to direct fluid away from the heat-generating structure to extract the heat and/or to draw the fluid toward the cooling element. In some embodiments, the exhaust system includes ducting configured to direct the fluid away from the heat-generating structure. The cooling system may have a total thickness of not more than three millimeters. In some embodiments, the system is incorporated into a mobile device.

In some embodiments, the system includes an inlet vent and an outlet vent. In such embodiment, the exhaust system is configured to direct the fluid from the heat-generating structure(s) toward the outlet vent. The cooling system is also configured to draw the fluid from the inlet vent toward the cooling element. The exhaust system may be configured to direct the fluid in a path past a plurality of components to the outlet vent. In some embodiments, the cooling system also includes an inlet subsystem and/or an outlet subsystem. The inlet subsystem includes an inlet cooling element in communication with the fluid. The inlet cooling element is configured to draw the fluid from the inlet vent using a first vibrational motion. The outlet subsystem includes an outlet cooling element in communication with the fluid. The outlet cooling element is configured to drive the fluid toward the outlet vent using a second vibrational motion.

In some embodiments, the cooling element has a first side distal from the heat-generating structure(s) and a second side proximal to the heat-generating structure(s). The exhaust system may also include chimneys and ducting. The chimneys are configured to direct the fluid from the heat-generating structure(s) toward the first side of the cooling element. The ducting is fluidically coupled with the chimneys and configured to direct the fluid from the chimneys to a location distal from the first side of the cooling element. In some such embodiments, the ducting is further configured to direct the fluid in a direction toward the heat-generating structure. For example, the heat-generating structure may include a heat spreader having an aperture therein. The ducting may be configured to direct the fluid through the aperture.

A system for cooling heat-generating structure(s) is also described. The cooling system includes cooling cells and an exhaust system. Each of the cooling cells includes a cooling element in communication with a fluid. The cooling element is configured to use vibrational motion to direct the fluid toward the heat-generating structure to extract heat from the heat-generating structure. The exhaust system is configured to direct fluid away from the heat-generating structure to extract the heat and/or to draw the fluid toward the cooling plurality of cooling cells.

The system may include an inlet vent and/or an outlet vent. The system is configured to draw the fluid from the inlet vent toward the cooling cells. The exhaust system is configured to direct the fluid from at least one heat-generating structure to the outlet vent. In some embodiments, the system includes an inlet subsystem and/or an outlet subsystem. The inlet subsystem includes an inlet cooling element in communication with the fluid. The inlet cooling element is configured to draw the fluid from the inlet vent using a first vibrational motion. The outlet subsystem includes an outlet cooling element in communication with the fluid. The outlet cooling element is configured to drive the fluid toward the outlet vent using a second vibrational motion. In some embodiments, the exhaust system includes ducting configured to direct the fluid away from the heat-generating structure(s). In some embodiments, the cooling cells have a total thickness of not more than three millimeters.

In some embodiments, the cooling element has a first side distal from the at least one heat-generating structure and a second side proximal to the heat-generating structure(s). The exhaust system may further include chimneys and ducting. The chimneys are configured to direct the fluid from the heat-generating structure(s) toward the first side of the cooling element. The ducting is fluidically coupled with the chimneys and configured to direct the fluid from the chimneys to a location distal from the first side of the cooling element. In some embodiments, the heat-generating structure includes a heat spreader having an aperture therein and ducting is configured to direct the fluid through the aperture.

A method is described. The method includes driving a cooling element to induce vibrational motion at a frequency. The cooling element is in communication with a fluid and configured to direct the fluid toward at least one heat-generating structure using the vibrational motion. The method also includes using an exhaust system to direct fluid away from the at least one heat-generating structure to extract heat and/or drawing the fluid toward the cooling element. In some embodiments, the exhaust system directs the fluid from the heat-generating structure(s) past components to an outlet vent. In some embodiments, the fluid is drawn from an inlet vent toward the cooling element.

FIGS. 1A-1E are diagrams depicting an exemplary embodiment of active cooling system 100 usable with heat-generating structure 102 and including a centrally anchored cooling element 120. For clarity, only certain components are shown. FIGS. 1A-1E are not to scale. Although shown as symmetric, cooling system 100 need not be.

Cooling system 100 includes top plate 110 having vent 112 therein, cooling element 120, orifice plate 130 having orifices 132 therein, support structure (or “anchor”) 160 and chambers 140 and 150 (collectively chamber 140/150) formed therein. Cooling element 120 is supported at its central region by anchor 160. Regions of cooling element 120 closer to and including portions of the cooling element's perimeter (e.g. tip 121) vibrate when actuated. In some embodiments, tip 121 of cooling element 120 includes a portion of the perimeter furthest from anchor 160 and undergoes the largest deflection during actuation of cooling element 120. For clarity, only one tip 121 of cooling element 120 is labeled in FIG. 1A.

FIG. 1A depicts cooling system 100 in a neutral position. Thus, cooling element 120 is shown as substantially flat. For in-phase operation, cooling element 120 is driven to vibrate between positions shown in FIGS. 1B and 1C. This vibrational motion draws fluid (e.g. air) into vent 112, through chambers 140 and 150 and out orifices 132 at high speed and/or flow rates. For example, the speed at which the fluid impinges on heat-generating structure 102 may be at least thirty meters per second. In some embodiments, the fluid is driven by cooling element 120 toward heat-generating structure 102 at a speed of at least forty-five meters per second. In some embodiments, the fluid is driven toward heat-generating structure 102 by cooling element 120 at speeds of at least sixty meters per second. Other speeds may be possible in some embodiments. Cooling system 100 is also configured so that little or no fluid is drawn back into chamber 140/150 through orifices 132 by the vibrational motion of cooling element 120.

Heat-generating structure 102 is desired to be cooled by cooling system 100. In some embodiments, heat-generating structure 102 generates heat. For example, heat-generating structure may be an integrated circuit. In some embodiments, heat-generating structure 102 is desired to be cooled but does not generate heat itself. Heat-generating structure 102 may conduct heat (e.g. from a nearby object that generates heat). For example, heat-generating structure 102 might be a heat spreader or a vapor chamber. Thus, heat-generating structure 102 may include semiconductor components(s) including individual integrated circuit components such as processors, other integrated circuit(s) and/or chip package(s); sensor(s); optical device(s); one or more batteries; other component(s) of an electronic device such as a computing device; heat spreaders; heat pipes; other electronic component(s) and/or other device(s) desired to be cooled.

The devices in which cooling system 100 is desired to be used may also have limited space in which to place a cooling system. For example, cooling system 100 may be used in computing devices. Such computing devices may include but are not limited to smartphones, tablet computers, laptop computers, tablets, two-in-one laptops, hand held gaming systems, digital cameras, virtual reality headsets, augmented reality headsets, mixed reality headsets and other devices that are thin. Cooling system 100 may be a micro-electro-mechanical system (MEMS) cooling system capable of residing within mobile computing devices and/or other devices having limited space in at least one dimension. For example, the total height of cooling system 100 (from the top of heat-generating structure 102 to the top of top plate 110) may be less than 2 millimeters. In some embodiments, the total height of cooling system 100 is not more than 1.5 millimeters. In some embodiments, this total height is not more than 1.1 millimeters. In some embodiments, the total height does not exceed one millimeter. In some embodiments, the total height does not exceed two hundred and fifty micrometers. Similarly, the distance between the bottom of orifice plate 130 and the top of heat-generating structure 102, y, may be small. In some embodiments, y is at least two hundred micrometers and not more than one millimeter. In some embodiments, y is at least two hundred micrometers and not more than three hundred micrometers. Thus, cooling system 100 is usable computing devices and/or other devices having limited space in at least one dimension. However, nothing prevents the use of cooling system 100 in devices having fewer limitations on space and/or for purposes other than cooling. Although one cooling system 100 is shown (e.g. one cooling cell), multiple cooling systems 100 might be used in connection with heat-generating structure 102. For example, a one or two-dimensional array of cooling cells might be utilized.

Cooling system 100 is in communication with a fluid used to cool heat-generating structure 102. The fluid may be a gas or a liquid. For example, the fluid may be air. In some embodiments, the fluid includes fluid from outside of the device in which cooling system 100 resides (e.g. provided through external vents in the device). In some embodiments, the fluid circulates within the device in which cooling system resides (e.g. in an enclosed device).

Cooling element 120 can be considered to divide the interior of active cooling system 100 into top chamber 140 and bottom chamber 150. Top chamber 140 is formed by cooling element 120, the sides, and top plate 110. Bottom chamber 150 is formed by orifice plate 130, the sides, cooling element 120 and anchor 160. Top chamber 140 and bottom chamber 150 are connected at the periphery of cooling element 120 and together form chamber 140/150 (e.g. an interior chamber of cooling system 100).

The size and configuration of top chamber 140 may be a function of the cell (cooling system 100) dimensions, cooling element 120 motion, and the frequency of operation. Top chamber 140 has a height, h1. The height of top chamber 140 may be selected to provide sufficient pressure to drive the fluid to bottom chamber 140 and through orifices 132 at the desired flow rate and/or speed. Top chamber 140 is also sufficiently tall that cooling element 120 does not contact top plate 140 when actuated. In some embodiments, the height of top chamber 140 is at least fifty micrometers and not more than five hundred micrometers. In some embodiments, top chamber 140 has a height of at least two hundred and not more than three hundred micrometers.

Bottom chamber 150 has a height, h2. In some embodiments, the height of bottom chamber 150 is sufficient to accommodate the motion of cooling element 120. Thus, no portion of cooling element 120 contacts orifice plate 130 during normal operation. Bottom chamber 150 is generally smaller than top chamber 140 and may aid in reducing the backflow of fluid into orifices 132. In some embodiments, the height of bottom chamber 150 is the maximum deflection of cooling element 120 plus at least five micrometers and not more than ten micrometers. In some embodiments, the deflection of cooling element 120 (e.g. the deflection of tip 121) has an amplitude of at least ten micrometers and not more than one hundred micrometers. In some such embodiments, the amplitude of deflection of cooling element 120 is at least ten micrometers and not more than sixty micrometers. However, the amplitude of deflection of cooling element 120 depends on factors such as the desired flow rate through cooling system 100 and the configuration of cooling system 100. Thus, the height of bottom chamber 150 generally depends on the flow rate through and other components of cooling system 100.

Top plate 110 includes vent 112 through which fluid may be drawn into cooling system 100. Top vent 112 may have a size chosen based on the desired the acoustic pressure in chamber 140. For example, in some embodiments, the width, w, of vent 112 is at least five hundred micrometers and not more than one thousand micrometers. In some embodiments, the width of vent 112 is at least two hundred fifty micrometers and not more than two thousand micrometers. In the embodiment shown, vent 112 is a centrally located aperture in top plate 110. In other embodiments, vent 112 may be located elsewhere. For example, vent 112 may be closer to one of the edges of top plate 110. Vent 112 may have a circular, rectangular or other shaped footprint. Although a single vent 112 is shown, multiple vents might be used. For example, vents may be offset toward the edges of top chamber 140 or be located on the side(s) of top chamber 140. Although top plate 110 is shown as substantially flat, in some embodiments trenches and/or other structures may be provided in top plate 110 to modify the configuration of top chamber 140 and/or the region above top plate 110.

Anchor (support structure) 160 supports cooling element 120 at the central portion of cooling element 120. Thus, at least part of the perimeter of cooling element 120 is unpinned and free to vibrate. In some embodiments, anchor 160 extends along a central axis of cooling element 120 (e.g. perpendicular to the page in FIGS. 1A-1E). In such embodiments, portions of cooling element 120 that vibrate (e.g. including tip 121) move in a cantilevered fashion. Thus, portions of cooling element 120 may move in a manner analogous to the wings of a butterfly (i.e. in phase) and/or analogous to a seesaw (i.e. out of phase). Thus, the portions of cooling element 120 that vibrate in a cantilevered fashion do so in phase in some embodiments and out of phase in other embodiments. In some embodiments, anchor 160 does not extend along an axis of cooling element 120. In such embodiments, all portions of the perimeter of cooling element 120 are free to vibrate (e.g. analogous to a jellyfish). In the embodiment shown, anchor 160 supports cooling element 120 from the bottom of cooling element 120. In other embodiments, anchor 160 may support cooling element 120 in another manner. For example, anchor 160 may support cooling element 120 from the top (e.g. cooling element 120 hangs from anchor 160). In some embodiments, the width, a, of anchor 160 is at least 0.5 millimeters and not more than four millimeters. In some embodiments, the width of anchor 160 is at least two millimeters and not more than 2.5 millimeters. Anchor 160 may occupy at least ten percent and not more than fifty percent of cooling element 120.

Cooling element 120 has a first side distal from heat-generating structure 102 and a second side proximate to heat-generating structure 102. In the embodiment shown in FIGS. 1A-1E, the first side of cooling element 120 is the top of cooling element 120 (closer to top plate 110) and the second side is the bottom of cooling element 120 (closer to orifice plate 130). Cooling element 120 is actuated to undergo vibrational motion as shown in FIGS. 1A-1E. The vibrational motion of cooling element 120 drives fluid from the first side of cooling element 120 distal from heat-generating structure 102 (e.g. from top chamber 140) to a second side of cooling element 120 proximate to heat-generating structure 102 (e.g. to bottom chamber 150). The vibrational motion of cooling element 120 also draws fluid through vent 112 and into top chamber 140; forces fluid from top chamber 140 to bottom chamber 150; and drives fluid from bottom chamber 140 through orifices 132 of orifice plate 130.

Cooling element 120 has a length, L, that depends upon the frequency at which cooling element 120 is desired to vibrate. In some embodiments, the length of cooling element 120 is at least four millimeters and not more than ten millimeters. In some such embodiments, cooling element 120 has a length of at least six millimeters and not more than eight millimeters. The depth of cooling element 120 (e.g. perpendicular to the plane shown in FIGS. 1A-1E) may vary from one fourth of L through twice L. For example, cooling element 120 may have the same depth as length. The thickness, t, of cooling element 120 may vary based upon the configuration of cooling element 120 and/or the frequency at which cooling element 120 is desired to be actuated. In some embodiments, the cooling element thickness is at least two hundred micrometers and not more than three hundred and fifty micrometers for cooling element 120 having a length of eight millimeters and driven at a frequency of at least twenty kilohertz and not more than twenty-five kilohertz. The length, C of chamber 140/150 is close to the length, L, of cooling element 120. For example, in some embodiments, the distance, d, between the edge of cooling element 120 and the wall of chamber 140/50 is at least one hundred micrometers and not more than five hundred micrometers. In some embodiments, d is at least two hundred micrometers and not more than three hundred micrometers.

Cooling element 120 may be driven at a frequency that is at or near both the resonant frequency for an acoustic resonance of a pressure wave of the fluid in top chamber 140 and the resonant frequency for a structural resonance of cooling element 120. The portion of cooling element 120 undergoing vibrational motion is driven at or near resonance (the “structural resonance”) of cooling element 120. This portion of cooling element 120 undergoing vibration may be a cantilevered section in some embodiments. The frequency of vibration for structural resonance is termed the structural resonant frequency. Use of the structural resonant frequency in driving cooling element 112 reduces the power consumption of cooling system 100. Cooling element 120 and top chamber 140 may also be configured such that this structural resonant frequency corresponds to a resonance in a pressure wave in the fluid being driven through top chamber 140 (the acoustic resonance of top chamber 140). The frequency of such a pressure wave is termed the acoustic resonant frequency. At acoustic resonance, a node in pressure occurs near vent 112 and an antinode in pressure occurs near the periphery of cooling system 100 (e.g. near tip 121 of cooling element 120 and near the connection between top chamber 140 and bottom chamber 150). The distance between these two regions is C/2. Thus, C/2=nλ/4, where λ is the acoustic wavelength for the fluid and n is odd (e.g. n=1, 3, 5, etc.). For the lowest order mode, C=λ/2. Because the length of chamber 140 (e.g. C) is close to the length of cooling element 120, in some embodiments, it is also approximately true that L/2=nλ/4, where λ is the acoustic wavelength for the fluid and n is odd. Thus, the frequency at which cooling element 120 is driven, v, is at or near the structural resonant frequency for cooling element 120. The frequency v is also at or near the acoustic resonant frequency for at least top chamber 140. The acoustic resonant frequency of top chamber 140 generally varies less dramatically with parameters such as temperature and size than the structural resonant frequency of cooling element 120. Consequently, in some embodiments, cooling element 120 may be driven at (or closer to) a structural resonant frequency than to the acoustic resonant frequency.

Orifice plate 130 has orifices 132 therein. Although a particular number and distribution of orifices 132 are shown, another number and/or another distribution may be used. A single orifice plate 130 is used for a single cooling system 100. In other embodiments, multiple cooling systems 100 may share an orifice plate. For example, multiple cells 100 may be provided together in a desired configuration. In such embodiments, the cells 100 may be the same size and configuration or different size(s) and/or configuration(s). Orifices 132 are shown as having an axis oriented normal to a surface of heat-generating structure 102. In other embodiments, the axis of one or more orifices 132 may be at another angle. For example, the angle of the axis may be selected from substantially zero degrees and a nonzero acute angle. Orifices 132 also have sidewalls that are substantially parallel to the normal to the surface of orifice plate 130. In some, orifices may have sidewalls at a nonzero angle to the normal to the surface of orifice plate 130. For example, orifices 132 may be cone-shaped. Further, although orifice place 130 is shown as substantially flat, in some embodiments, trenches and/or other structures may be provided in orifice plate 130 to modify the configuration of bottom chamber 150 and/or the region between orifice plate 130 and heat-generating structure 102.

The size, distribution and locations of orifices 132 are chosen to control the flow rate of fluid driven to the surface of heat-generating structure 102. The locations and configurations of orifices 132 may be configured to increase/maximize the fluid flow from bottom chamber 150 through orifices 132 to the jet channel (the region between the bottom of orifice plate 130 and the top of heat-generating structure 102). The locations and configurations of orifices 132 may also be selected to reduce/minimize the suction flow (e.g. back flow) from the jet channel through orifices 132. For example, the locations of orifices are desired to be sufficiently far from tip 121 that suction in the upstroke of cooling element 120 (tip 121 moves away from orifice plate 13) that would pull fluid into bottom chamber 150 through orifices 132 is reduced. The locations of orifices are also desired to be sufficiently close to tip 121 that suction in the upstroke of cooling element 120 also allows a higher pressure from top chamber 140 to push fluid from top chamber 140 into bottom chamber 150. In some embodiments, the ratio of the flow rate from top chamber 140 into bottom chamber 150 to the flow rate from the jet channel through orifices 132 in the upstroke (the “net flow ratio”) is greater than 2:1. In some embodiments, the net flow ratio is at least 85:15. In some embodiments, the net flow ratio is at least 90:10. In order to provide the desired pressure, flow rate, suction, and net flow ratio, orifices 132 are desired to be at least a distance, r1, from tip 121 and not more than a distance, r2, from tip 121 of cooling element 120. In some embodiments r1 is at least one hundred micrometers (e.g. r1≥100 μm) and r2 is not more than one millimeter (e.g. r2≤1000 μm). In some embodiments, orifices 132 are at least two hundred micrometers from tip 121 of cooling element 120 (e.g. r1≥200 μm). In some such embodiments, orifices 132 are at least three hundred micrometers from tip 121 of cooling element 120 (e.g. r1≥300 μm). In some embodiments, orifices 132 have a width of at least one hundred micrometers and not more than five hundred micrometers. In some embodiments, orifices 132 have a width of at least two hundred micrometers and not more than three hundred micrometers. In some embodiments, the orifice separation, s, is at least one hundred micrometers and not more than one millimeter. In some such embodiments, the orifice separation is at least four hundred micrometers and not more than six hundred micrometers. In some embodiments, orifices 132 are also desired to occupy a particular fraction of the area of orifice plate 130. For example, orifices 132 may cover at least five percent and not more than fifteen percent of the footprint of orifice plate 130 in order to achieve a desired flow rate of fluid through orifices 132. In some embodiments, orifices 132 cover at least eight percent and not more than twelve percent of the footprint of orifice plate 130.

In some embodiments, cooling element 120 is actuated using a piezoelectric. Thus, cooling element 120 may be a piezoelectric cooling element. Cooling element 120 may be driven by a piezoelectric that is mounted on or integrated into cooling element 120. In some embodiments, cooling element 120 is driven in another manner including but not limited to providing a piezoelectric on another structure in cooling system 100. Cooling element 120 and analogous cooling elements are referred to hereinafter as piezoelectric cooling element though it is possible that a mechanism other than a piezoelectric might be used to drive the cooling element. In some embodiments, cooling element 120 includes a piezoelectric layer on substrate. The substrate may be a stainless steel, Ni alloy and/or Hastelloy substrate. In some embodiments, piezoelectric layer includes multiple sublayers formed as thin films on the substrate. In other embodiments, the piezoelectric layer may be a bulk layer affixed to the substrate. Such a piezoelectric cooling element 120 also includes electrodes used to activate the piezoelectric. The substrate functions as an electrode in some embodiments. In other embodiments, a bottom electrode may be provided between the substrate and the piezoelectric layer. Other layers including but not limited to seed, capping, passivation or other layers might be included in piezoelectric cooling element. Thus, cooling element 120 may be actuated using a piezoelectric.

In some embodiments, cooling system 100 includes chimneys (not shown) or other ducting. Such ducting provides a path for heated fluid to flow away from heat-generating structure 102. In some embodiments, ducting returns fluid to the side of top plate 110 distal from heat-generating structure 102. In some embodiments, ducting may instead directed fluid away from heat-generating structure 102 in a direction parallel to heat-generating structure 102 or perpendicular to heat-generating structure 102 but in the opposite direction (e.g. toward the bottom of the page). For a device in which fluid external to the device is used in cooling system 100, the ducting may channel the heated fluid to a vent. In such embodiments, additional fluid may be provided from an inlet vent. In embodiments, in which the device is enclosed, the ducting may provide a circuitous path back to the region near vent 112 and distal from heat-generating structure 102. Such a path allows for the fluid to dissipate heat before being reused to cool heat-generating structure 102. In other embodiments, ducting may be omitted or configured in another manner. Thus, the fluid is allowed to carry away heat from heat-generating structure 102.

Operation of cooling system 100 is described in the context of FIGS. 1A-1E. Although described in the context of particular pressures, gap sizes, and timing of flow, operation of cooling system 100 is not dependent upon the explanation herein. FIGS. 1B-1C depict in-phase operation of cooling system 100. Referring to FIG. 1B, cooling element 120 has been actuated so that its tip 121 moves away from top plate 110. FIG. 1B can thus be considered to depict the end of a down stroke of cooling element 120. Because of the vibrational motion of cooling element 120, gap 152 for bottom chamber 150 has decreased in size and is shown as gap 152B. Conversely, gap 142 for top chamber 140 has increased in size and is shown as gap 142B. During the down stroke, a lower (e.g. minimum) pressure is developed at the periphery when cooling element 120 is at the neutral position. As the down stroke continues, bottom chamber 150 decreases in size and top chamber 140 increases in size as shown in FIG. 1B. Thus, fluid is driven out of orifices 132 in a direction that is at or near perpendicular to the surface of orifice plate 130 and/or the top surface of heat-generating structure 102. The fluid is driven from orifices 132 toward heat-generating structure 102 at a high speed, for example in excess of thirty-five meters per second. In some embodiments, the fluid then travels along the surface of heat-generating structure 102 and toward the periphery of heat-generating structure 102, where the pressure is lower than near orifices 132. Also in the down stroke, top chamber 140 increases in size and a lower pressure is present in top chamber 140. As a result, fluid is drawn into top chamber 140 through vent 112. The motion of the fluid into vent 112, through orifices 132, and along the surface of heat-generating structure 102 is shown by unlabeled arrows in FIG. 1B.

Cooling element 120 is also actuated so that top 121 moves away from heat-generating structure 102 and toward top plate 110. FIG. 1C can thus be considered to depict the end of an up stroke of cooling element 120. Because of the motion of cooling element 120, gap 142 has decreased in size and is shown as gap 142C. Gap 152 has increased in size and is shown as gap 152C. During the upstroke, a higher (e.g. maximum) pressure is developed at the periphery when cooling element 120 is at the neutral position. As the upstroke continues, bottom chamber 150 increases in size and top chamber 140 decreases in size as shown in FIG. 1C. Thus, the fluid is driven from top chamber 140 (e.g. the periphery of chamber 140/150) to bottom chamber 150. Thus, when tip 121 of cooling element 120 moves up, top chamber 140 serves as a nozzle for the entering fluid to speed up and be driven towards bottom chamber 150. The motion of the fluid into bottom chamber 150 is shown by unlabeled arrows in FIG. 1C. The location and configuration of cooling element 120 and orifices 132 are selected to reduce suction and, therefore, back flow of fluid from the jet channel (between heat-generating structure 102 and orifice plate 130) into orifices 132 during the upstroke. Thus, cooling system 100 is able to drive fluid from top chamber 140 to bottom chamber 150 without an undue amount of backflow of heated fluid from the jet channel entering bottom chamber 10.

The motion between the positions shown in FIGS. 1B and 1C is repeated. Thus, cooling element 120 undergoes vibrational motion indicated in FIGS. 1A-1C, drawing fluid through vent 112 from the distal side of top plate 110 into top chamber 140; transferring fluid from top chamber 140 to bottom chamber 150; and pushing the fluid through orifices 132 and toward heat-generating structure 102. As discussed above, cooling element 120 is driven to vibrate at or near the structural resonant frequency of cooling element 120. Further, the structural resonant frequency of cooling element 120 is configured to align with the acoustic resonance of the chamber 140/150. The structural and acoustic resonant frequencies are generally chosen to be in the ultrasonic range. For example, the vibrational motion of cooling element 120 may be at frequencies from 15 kHz through 30 kHz. In some embodiments, cooling element 120 vibrates at a frequency/frequencies of at least 20 kHz and not more than 30 kHz. The structural resonant frequency of cooling element 120 is within ten percent of the acoustic resonant frequency of cooling system 100. In some embodiments, the structural resonant frequency of cooling element 120 is within five percent of the acoustic resonant frequency of cooling system 100. In some embodiments, the structural resonant frequency of cooling element 120 is within three percent of the acoustic resonant frequency of cooling system 100. Consequently, efficiency and flow rate may be enhanced. However, other frequencies may be used.

Fluid driven toward heat-generating structure 102 may move substantially normal (perpendicular) to the top surface of heat-generating structure 102. In some embodiments, the fluid motion may have a nonzero acute angle with respect to the normal to the top surface of heat-generating structure 102. In either case, the fluid may thin and/or form apertures in the boundary layer of fluid at heat-generating structure 102. As a result, transfer of heat from heat-generating structure 102 may be improved. The fluid deflects off of heat-generating structure 102, traveling along the surface of heat-generating structure 102. In some embodiments, the fluid moves in a direction substantially parallel to the top of heat-generating structure 102. Thus, heat from heat-generating structure 102 may be extracted by the fluid. The fluid may exit the region between orifice plate 130 and heat-generating structure 102 at the edges of cooling system 100. Chimneys or other ducting (not shown) at the edges of cooling system 100 allow fluid to be carried away from heat-generating structure 102. In other embodiments, heated fluid may be transferred further from heat-generating structure 102 in another manner. The fluid may exchange the heat transferred from heat-generating structure 102 to another structure or to the ambient environment. Thus, fluid at the distal side of top plate 110 may remain relatively cool, allowing for the additional extraction of heat. In some embodiments, fluid is circulated, returning to distal side of top plate 110 after cooling. In other embodiments, heated fluid is carried away and replaced by new fluid at the distal side of cooling element 110. As a result, heat-generating structure 102 may be cooled.

FIGS. 1D-1E depict an embodiment of active cooling system 100 including centrally anchored cooling element 120 in which the cooling element is driven out-of-phase. More specifically, sections of cooling element 120 on opposite sides of anchor 160 (and thus on opposite sides of the central region of cooling element 120 that is supported by anchor 160) are driven to vibrate out-of-phase. In some embodiments, sections of cooling element 120 on opposite sides of anchor 160 are driven at or near one hundred and eighty degrees out-of-phase. Thus, one section of cooling element 120 vibrates toward top plate 110, while the other section of cooling element 120 vibrates toward orifice plate 130/heat-generating structure 102. Movement of a section of cooling element 120 toward top plate 110 (an upstroke) drives fluid in top cavity 140 to bottom cavity 150 on that side of anchor 160. Movement of a section of cooling element 120 toward orifice plate 130 drives fluid through orifices 132 and toward heat-generating structure 102. Thus, fluid traveling at high speeds (e.g. speeds described with respect to in-phase operation) is alternately driven out of orifices 132 on opposing sides of anchor 160. The movement of fluid is shown by unlabeled arrows in FIGS. 1D and 1E.

The motion between the positions shown in FIGS. 1D and 1E is repeated. Thus, cooling element 120 undergoes vibrational motion indicated in FIGS. 1A, 1D, and 1E, alternately drawing fluid through vent 112 from the distal side of top plate 110 into top chamber 140 for each side of cooling element 120; transferring fluid from each side of top chamber 140 to the corresponding side of bottom chamber 150; and pushing the fluid through orifices 132 on each side of anchor 160 and toward heat-generating structure 102. As discussed above, cooling element 120 is driven to vibrate at or near the structural resonant frequency of cooling element 120. Further, the structural resonant frequency of cooling element 120 is configured to align with the acoustic resonance of the chamber 140/150. The structural and acoustic resonant frequencies are generally chosen to be in the ultrasonic range. For example, the vibrational motion of cooling element 120 may be at the frequencies described for in-phase vibration. The structural resonant frequency of cooling element 120 is within ten percent of the acoustic resonant frequency of cooling system 100. In some embodiments, the structural resonant frequency of cooling element 120 is within five percent of the acoustic resonant frequency of cooling system 100. In some embodiments, the structural resonant frequency of cooling element 120 is within three percent of the acoustic resonant frequency of cooling system 100. Consequently, efficiency and flow rate may be enhanced. However, other frequencies may be used.

Fluid driven toward heat-generating structure 102 for out-of-phase vibration may move substantially normal (perpendicular) to the top surface of heat-generating structure 102, in a manner analogous to that described above for in-phase operation. Similarly, chimneys or other ducting (not shown) at the edges of cooling system 100 allow fluid to be carried away from heat-generating structure 102. In other embodiments, heated fluid may be transferred further from heat-generating structure 102 in another manner. The fluid may exchange the heat transferred from heat-generating structure 102 to another structure or to the ambient environment. Thus, fluid at the distal side of top plate 110 may remain relatively cool, allowing for the additional extraction of heat. In some embodiments, fluid is circulated, returning to distal side of top plate 110 after cooling. In other embodiments, heated fluid is carried away and replaced by new fluid at the distal side of cooling element 110. As a result, heat-generating structure 102 may be cooled.

Using the cooling system 100 actuated for in-phase vibration or out-of-phase vibration, fluid drawn in through vent 112 and driven through orifices 132 may efficiently dissipate heat from heat-generating structure 102. Because fluid impinges upon the heat-generating structure with sufficient speed (e.g. at least thirty meters per second) and in some embodiments substantially normal to the heat-generating structure, the boundary layer of fluid at the heat-generating structure may be thinned and/or partially removed. Consequently, heat transfer between heat-generating structure 102 and the moving fluid is improved. Because the heat-generating structure is more efficiently cooled, the corresponding integrated circuit may be run at higher speed and/or power for longer times. For example, if the heat-generating structure corresponds to a high-speed processor, such a processor may be run for longer times before throttling. Thus, performance of a device utilizing cooling system 100 may be improved. Further, cooling system 100 may be a MEMS device. Consequently, cooling systems 100 may be suitable for use in smaller and/or mobile devices, such as smart phones, other mobile phones, virtual reality headsets, tablets, two-in-one computers, wearables and handheld games, in which limited space is available. Performance of such devices may thus be improved. Because cooling element 120 may be vibrated at frequencies of 15 kHz or more, users may not hear any noise associated with actuation of cooling elements. If driven at or near structural and/or acoustic resonant frequencies, the power used in operating cooling systems may be significantly reduced. Cooling element 120 does not physically contact top plate 110 or orifice plate 130 during vibration. Thus, resonance of cooling element 120 may be more readily maintained. More specifically, physical contact between cooling element 120 and other structures disturbs the resonance conditions for cooling element 120. Disturbing these conditions may drive cooling element 120 out of resonance. Thus, additional power would need to be used to maintain actuation of cooling element 120. Further, the flow of fluid driven by cooling element 120 may decrease. These, issues are avoided through the use of pressure differentials and fluid flow as discussed above. The benefits of improved, quiet cooling may be achieved with limited additional power. Further, out-of-phase vibration of cooling element 120 allows the position of the center of mass of cooling element 100 to remain more stable. Although a torque is exerted on cooling element 120, the force due to the motion of the center of mass is reduced or eliminated. As a result, vibrations due to the motion of cooling element 120 may be reduced. Moreover, efficiency of cooling system 100 may be improved through the use of out-of-phase vibrational motion for the two sides of cooling element 120. Consequently, performance of devices incorporating the cooling system 100 may be improved. Further, cooling system 100 may be usable in other applications (e.g. with or without heat-generating structure 102) in which high fluid flows and/or velocities are desired.

FIGS. 2A-2B depict plan views of embodiments of cooling systems 200A and 200B analogous to active cooling systems such as cooling system 100. FIGS. 2A and 2B are not to scale. For simplicity, only portions of cooling elements 220A and 220B and anchors 260A and 260B, respectively, are shown. Cooling elements 220A and 220B are analogous to cooling element 120. Thus, the sizes and/or materials used for cooling elements 220A and/or 220B may be analogous to those for cooling element 120. Anchors (support structures) 260A and 260B are analogous to anchor 160 and are indicated by dashed lines.

For cooling elements 220A and 220B, anchors 260A and 260B are centrally located and extend along a central axis of cooling elements 220A and 220B, respectively. Thus, the cantilevered portions that are actuated to vibrate are to the right and left of anchors 260A and 260B. In some embodiments, cooling element(s) 220A and/or 220B are continuous structures, two portions of which are actuated (e.g. the cantilevered portions outside of anchors 260A and 260B). In some embodiments, cooling element(s) 220A and/or 220B include separate cantilevered portions each of which is attached to the anchors 260A and 260B, respectively, and actuated. Cantilevered portions of cooling elements 220A and 220B may thus be configured to vibrate in a manner analogous to the wings of a butterfly (in-phase) or to a seesaw (out-of-phase). In FIGS. 2A and 2B, L is the length of the cooling element, analogous to that depicted in FIGS. 1A-1E. Also in FIGS. 2A and 2B, the depth, P, of cooling elements 220A and 220B is indicated.

Also shown by dotted lines in FIGS. 2A-2B are piezoelectric 223. Piezoelectric 223 is used to actuate cooling elements 220A and 220B. In some embodiments, piezoelectric 223 may be located in another region and/or have a different configuration. Although described in the context of a piezoelectric, another mechanism for actuating cooling elements 260A and 260B can be utilized. Such other mechanisms may be at the locations of piezoelectric 223 or may be located elsewhere. In cooling element 260A, piezoelectric 223 may be affixed to cantilevered portions or may be integrated into cooling element 220A. Further, although piezoelectric 223 is shown as having particular shapes and sizes in FIGS. 2A and 2B, other configurations may be used.

In the embodiment shown in FIG. 2A, anchor 260A extends the entire depth of cooling element 220A. Thus, a portion of the perimeter of cooling element 260A is pinned. The unpinned portions of the perimeter of cooling element 260A are part of the cantilevered sections that undergo vibrational motion. In other embodiments, anchor need not extend the entire length of the central axis. In such embodiments, the entire perimeter of the cooling element is unpinned. However, such a cooling element still has cantilevered sections configured to vibrate in a manner described herein. For example, in FIG. 2B, anchor 260B does not extend to the perimeter of cooling element 220B. Thus, the perimeter of cooling element 220B is unpinned. However, anchor 260B still extends along the central axis of cooling element 220B. Cooling element 220B is still actuated such that cantilevered portions vibrate (e.g. analogous to the wings of a butterfly).

Although cooling element 220 A is depicted as rectangular, cooling elements may have another shape. In some embodiments, corners of cooling element 220A may be rounded. Cooling element 220B of FIG. 2B has rounded cantilevered sections. Other shapes are possible. In the embodiment shown in FIG. 2B, anchor 260B is hollow and includes apertures 263. In some embodiments, cooling element 220B has aperture(s) in the region of anchor 260B. In some embodiments, cooling element 220B includes multiple portions such that aperture(s) exist in the region of anchor 260B. As a result, fluid may be drawn through cooling element 220B and through anchor 260B. Thus, cooling element 220B may be used in place of a top plate, such as top plate 110. In such embodiments, apertures in cooling element 220B and apertures 263 may function in an analogous manner to vent 112. Further, although cooling elements 200A and 200B are depicted as being supported in a central region, in some embodiments, one cantilevered section of the cooling element 220A and/or 220B might be omitted. In such embodiments, cooling element 220A and/or 220B may be considered to be supported, or anchored, at or near one edge, while at least part of at least the opposing edge is free to undergo vibrational motion. In some such embodiments, the cooling element 220A and/or 220B may include a single cantilevered section that undergoes vibrational motion.

FIGS. 3A-3B depict plan views of embodiments of cooling systems 300A and 300B analogous to active cooling systems such as cooling system 100. FIGS. 3A and 3B are not to scale. For simplicity, only cooling elements 320A and 320B and anchors 360A and 360B, respectively, are shown. Cooling elements 320A and 320B are analogous to cooling element 120. Thus, the sizes and/or materials used for cooling elements 320A and/or 320B may be analogous to those for cooling element 120. Anchors 360A and 360B are analogous to anchor 160 and are indicated by dashed lines.

For cooling elements 320A and 320B, anchors 360A and 360B, respectively, are limited to a central region of cooling elements 320A and 320B, respectively. Thus, the regions surrounding anchors 360A and 360B undergo vibrational motion. Cooling elements 320A and 320B may thus be configured to vibrate in a manner analogous to a jellyfish or similar to the opening/closing of an umbrella. In some embodiments, the entire perimeter of cooling elements 320A and 320B vibrate in phase (e.g. all move up or down together). In other embodiments, portions of the perimeter of cooling elements 320A and 320B vibrate out of phase. In FIGS. 3A and 3B, L is the length (e.g. diameter) of the cooling element, analogous to that depicted in FIGS. 1A-1E. Although cooling elements 320A and 320B are depicted as circular, cooling elements may have another shape. Further, a piezoelectric (not shown in FIGS. 3A-3B) and/or other mechanism may be used to drive the vibrational motion of cooling elements 320A and 320B.

In the embodiment shown in FIG. 3B, the anchor 360B is hollow and has apertures 363. In some embodiments, cooling element 320B has aperture(s) in the region of anchor 360B. In some embodiments, cooling element 320B includes multiple portions such that aperture(s) exist in the region of anchor 360B. As a result, fluid may be drawn through cooling element 320B and through anchor 360B. The fluid may exit through apertures 363. Thus, cooling element 320B may be used in place of a top plate, such as top plate 110. In such embodiments, apertures in cooling element 320B and apertures 363 may function in an analogous manner to vent 112.

Cooling systems such as cooling system 100 can utilize cooling element(s) 220A, 220B, 320A, 320B and/or analogous cooling elements. Such cooling systems may also share the benefits of cooling system 100. Cooling systems using cooling element(s) 220A, 220B, 320A, 320B and/or analogous cooling elements may more efficiently drive fluid toward heat-generating structures at high speeds. Consequently, heat transfer between the heat-generating structure and the moving fluid is improved. Because the heat-generating structure is more efficiently cooled, the corresponding device may exhibit improved operation, such as running at higher speed and/or power for longer times. Cooling systems employing cooling element(s) 220A, 220B, 320A, 320B and/or analogous cooling elements may be suitable for use in smaller and/or mobile devices in which limited space is available. Performance of such devices may thus be improved. Because cooling element(s) 220A, 220B, 320A, 320B and/or analogous cooling elements may be vibrated at frequencies of 15 kHz or more, users may not hear any noise associated with actuation of cooling elements. If driven at or near the acoustic and/or structural resonance frequencies for the cooling element(s) 220A, 220B, 320A, 320B and/or analogous cooling elements, the power used in operating cooling systems may be significantly reduced. Cooling element(s) 220A, 220B, 320A, 320B and/or analogous cooling elements may not physically contact the plates during use, allowing resonance to be more readily maintained. The benefits of improved, quiet cooling may be achieved with limited additional power. Consequently, performance of devices incorporating the cooling element(s) 220A, 220B, 320A, 320B and/or analogous cooling elements may be improved.

In some embodiments, the cooling element may be anchored at one or more edges instead of at its center. For example, FIGS. 4A-4C depict an embodiment of cooling system 400 in which the edges of the cooling elements are anchored.

FIGS. 4A-4C are diagrams depicting an exemplary embodiment of active cooling system 400 usable with a heat-generating structure 402. For clarity, only certain components are shown and FIGS. 4A-4C are not to scale. Cooling system 400 is used in connection with a heat-generating structure 402. Although shown as symmetric, cooling system 400 need not be symmetric.

Cooling system 400 includes cooling elements 410 and 420. Cooling system 400 also includes orifice plate 430 having orifices 432 therein, top chamber 440 and bottom chamber 450 that may be analogous to orifice plate 130 having orifices 132 therein, top chamber 140 and bottom chamber 150. Also shown are optional chimneys 460 used to direct fluid.

Cooling element 410 has a first side distal from heat-generating structure 402 and a second side proximate to heat-generating structure 402. The first side of cooling element 410 is the top of cooling element 410 and the second side is the bottom of cooling element 410. Cooling element 410 also has a passive vent 412 therein. In the embodiment shown, passive vent 412 is a centrally located aperture in cooling element 410. In other embodiments, passive vent 412 may be located elsewhere. For example, passive vent 412 may be closer to one of the edges of cooling element 410. Passive vent 412 may have a circular, rectangular or other shaped footprint. Although one passive vent 412 is shown, multiple passive vents might be used.

Cooling element 420 is between cooling element 410 and heat-generating structure 402. In the embodiment shown, cooling element 420 is also between cooling element 410 and orifice plate 430. Cooling elements 410 and 420 are separated by gap 442 and form a top chamber 440. A bottom chamber 450 is formed between cooling element 420 and orifice plate 430. Cooling element 420 also has active vents 422 therein. In the embodiment shown, active vents 422 are apertures located away from the central region of cooling element 420. In other embodiments, active vents 422 may be located elsewhere. For example, an active vent may be centrally located in cooling element 420. Although two active vents 422 are shown, another number (e.g. one, three, etc.) might be present. In some embodiments, active vents 422 are positioned such that the active vents 422 are not aligned with passive vent 412. Active vents 422 may have circular, rectangular or other shaped footprints. In some embodiments, a single cooling element 410 or 420 which does not include a vent may be used in lieu of two cooling elements.

In some embodiments, cooling system 400 includes chimneys 460. Chimneys 460 provide a return path for heated fluid to flow away from heat-generating structure 402. In some embodiments, chimneys 460 return fluid to the side of cooling element 410 distal from heat-generating structure 402. In the embodiment shown, chimneys 460 direct heated fluid substantially perpendicular to heat-generating structure 402 and toward the side of cooling element 410 distal from heat-generating structure 402. In other embodiments, chimneys 460 may be omitted or configured in another manner. For example, chimneys may instead directed fluid away from heat-generating structure 402 in a direction parallel to heat-generating structure 402 or perpendicular to heat-generating structure 402 but opposite to the direction shown (e.g. toward the bottom of the page). If multiple cooling systems 400 are provided in an array, each cooling system 400 may include chimneys, only cooling systems 400 at the edges may include chimneys, other ducting may be provided at the edges or other locations in the array to provide a path for heated fluid to flow and/or other mechanisms may be used to allow heated fluid to be removed from the region proximate to heat-generating structure 402.

FIG. 4A depicts cooling system 400 in a neutral position. Thus, cooling elements 410 and 420 are shown as substantially flat. In operation, piezoelectric cooling elements 410 and 420 are actuated to vibrate between positions shown in FIGS. 4B and 4C. Piezoelectric cooling elements 410 and 420 are, therefore, piezoelectric actuators. Operation of cooling system 400 is described in the context of FIGS. 4B and 4C. Referring to FIG. 4B, piezoelectric cooling element 410 has been actuated to move away from (deform to be convex) heat-generating structure 402, while piezoelectric cooling element 420 has been actuated to move toward (deform to be concave) heat-generating structure 402. This configuration is referred to as the suction arrangement. Because of the vibrational motion of piezoelectric cooling elements 410 and 420, gap 442 has increased in size and is shown as gap 442A. For example, in some embodiments, gap 442 has a height of at least ten and not more than twenty micrometers in the neutral position (FIG. 4A). Gap 442A may have a height of at least twenty and not more than thirty micrometers in the suction arrangement (FIG. 4B). Thus, top chamber 440 has increased in volume, while bottom chamber 450 has decreased in volume. In the suction arrangement, the flow resistance of passive vent 412 (passive suction flow resistance) is low. Consequently, the pressure at passive vent 412 is low. In contrast, the flow resistance of active vent 422 (active suction flow resistance) is high. Consequently, the pressure at active vent 422 is high. Because of the low passive suction flow resistance, fluid is drawn into top chamber 440 through passive vent 412. This is shown by arrows in FIG. 4B. However, fluid does not flow out of (or flows out to a limited extent) active vent 422 because of the high passive suction flow resistance. However, active vent 422 is not physically closed in this configuration. For example, active vent 422 is not in contact with orifice plate 430 in the suction arrangement.

FIG. 4C depicts an expulsion arrangement. Piezoelectric cooling element 410 has been actuated to move toward (deform to be concave) heat-generating structure 402, while piezoelectric cooling element 420 has been actuated to move away from (deform to be convex) heat-generating structure 402. Because of the vibrational motion of piezoelectric cooling elements 410 and 420, gap 442 has decreased in size and is shown as gap 442B. For example, in some embodiments, gap 442 has a height of at least ten and not more than twenty micrometers in the neutral position (FIG. 4A). Gap 442B has a height of at least five and not more than ten micrometers in the expulsion arrangement (FIG. 4C). Thus, top chamber 440 has decreased in volume, while bottom chamber 450 has increased in volume. In the expulsion arrangement, the flow resistance of passive vent 412 (passive expulsion flow resistance) is high. Consequently, the pressure at passive vent 412 is high. In contrast, the flow resistance of active vent 422 (active expulsion flow resistance) is low. Consequently, the pressure at active vent 422 is low. Because of the low active expulsion flow resistance, fluid is expelled from top chamber 440 through active vent 422, into bottom chamber 450 and through orifices 432. This is shown by arrows in FIG. 4C. However, fluid does not flow out of (or flows out to a limited extent) passive vent 412 because of the high passive expulsion flow resistance. Thus, passive vent 412 is considered closed and active vent 422 is considered open in the expulsion arrangement. However passive vent 412 is not physically closed in this configuration. For example, passive vent 412 is not in contact with cooling element 420 in the expulsion arrangement. Gap 442B does not have a zero length.

Virtual valves may be considered to be formed at or near active vent 422 and passive vent 412. A virtual valve has a high, but not infinite, flow resistance when closed. Thus, a virtual valve does not physically block flow but instead uses a high flow resistance or high pressure to throttle or prevent flow. A virtual valve has a significantly lower flow resistance or pressure when open, allowing flow. In some embodiments, the ratio of flow resistances or pressures between closed and open for a virtual valve is at least three and not more than ten. Thus, active vent 422 and its virtual valve (“active virtual valve”) are considered closed in the suction arrangement because the flow resistance is sufficiently high that little or no fluid flows through active vent 422 in the suction arrangement. Passive vent 412 and its virtual valve (“passive virtual valve”) are considered open in the suction arrangement because the pressure or flow resistance is sufficiently low to allow fluid to be drawn in to top chamber 440 through passive vent 412. In contrast, active vent 422 and active virtual valve are considered open in the expulsion arrangement because the pressure or flow resistance is sufficiently low to allow fluid to flow through active vent 422 and be driven out of orifices 432. Passive vent 412 and passive virtual valve are considered closed in the expulsion arrangement because the pressure or flow resistance is sufficiently high that little to no fluid is drawn through passive vent 412 in the expulsion arrangement.

Due to the vibrational motion of cooling elements 410 and 420 (and the attendant decrease in gap 442A/442B from FIG. 4B to FIG. 4C), the fluid is drawn in to top chamber 440 and through orifices 432. The motion of the fluid is shown by arrows through orifices 432. The fluid may spread as it travels away from orifice plate 420, as shown by dashed lines and arrows for some orifices 432 in FIG. 4C. The fluid deflects off of heat-generating structure 402 and travels along the channel between heat-generating structure 402 and orifice plate 430.

The motion between the positions shown in FIGS. 4B and 4C may be repeated. Thus, piezoelectric cooling elements 410 and 420 vibrate, drawing fluid through passive vent 412 from the distal side of cooling element 410, into top chamber 440, out of chamber 440 through active vent 422 and pushing the fluid through orifices 432 and toward heat-generating structure 402. In some embodiments, the frequency/frequencies of vibration of cooling elements 410 and/or 420 are analogous to those of cooling element 120. Further, in some embodiments, piezoelectric cooling element(s) 410 and/or 420 may be driven at or near the resonant frequency. The resonant frequencies of piezoelectric cooling element(s) 410 and 420 may also be desired to be close. In some embodiments, the resonant frequencies of piezoelectric cooling element(s) 410 and 420 are desired to be within one hundred Hertz. In some embodiments, feedback is used to maintain piezoelectric cooling element(s) 410 and/or 420 at or near resonance. In some embodiments, the resonant frequencies of cooling elements 410 and/or 420 are closely matched to the acoustic resonant frequencies of chamber(s) 440 and/or 450. In some embodiments, the speed at which the fluid impinges on heat-generating structure 402 is in the ranges described herein for cooling system 100.

As indicated in FIG. 4C, the fluid driven toward heat-generating structure 402 may move substantially normal (perpendicular) to the top surface of heat-generating structure 402. In other embodiments, the fluid motion may have a nonzero acute angle with respect to the normal to the top surface of heat-generating structure 402. In either case, the fluid may thin and/or form apertures in the boundary layer of fluid at heat-generating structure 402. The boundary layer in one case is indicated by the curved dotted lines at the top surface of heat-generating structure 402 in FIG. 4C. As a result, transfer of heat from heat-generating structure 402 may be improved. The fluid deflects off of heat-generating structure 402, traveling along the surface of heat-generating structure 402. In some embodiments, the fluid moves in a direction substantially parallel to the top of heat-generating structure 402. Thus, heat from heat-generating structure 402 may be extracted by the fluid. The fluid may exit the region between orifice plate 430 and heat-generating structure 402 at the edges of cooling system 400. In the embodiment shown, chimneys 460 at the edges of cooling system 400 allow fluid to be carried away from heat-generating structure 402. In other embodiments, heated fluid may be transferred further from heat-generating structure 402 in another manner. The fluid may return to the distal side of cooling elements 410 where the fluid may exchange the heat transferred from heat-generating structure 402 to another structure or to the ambient environment. The fluid may then be circulated through cooling system 400 to extract additional heat. In other embodiments, heated fluid is carried away and replaced by new fluid at the distal side of cooling element 410. As a result, heat-generating structure 402 may be cooled.

Opening and closing of passive vent 412 (passive virtual valve) and active vent 422 (active virtual valve) to draw fluid into chamber 450 and expel fluid through orifices 432 is based upon dynamic changes to flow resistance. In some embodiments, the ratio of active suction flow resistance to active expulsion flow resistance is at least three. In some such embodiments, the ratio of active suction flow resistance to active expulsion flow resistance is not more than ten. In some embodiments, the ratio of passive expulsion flow resistance to passive suction flow resistance is at least three. In some such embodiments, the ratio of passive expulsion flow resistance to passive suction flow resistance is not more than ten. Thus, virtual valves corresponding to vents 410 and/or 420 may be opened and closed. These ratios of pressures may be considered to be due to the change in size of gap 442/442A/442B (e.g. five through thirty micrometers in some embodiments). In some embodiments, the difference in pressure between being open and closed is 0.1 atmosphere through 0.2 atmosphere. For example, the pressure at passive vent 412 in the suction arrangement may be at least 0.1 atmosphere and not more than 0.2 atmosphere less than the pressure at passive vent 412 in the expulsion arrangement. Similarly, the pressure at active vent 422 in the expulsion arrangement may be at least 0.1 atmosphere and not more than 0.2 atmosphere less than the pressure at active vent 422 in the suction arrangement.

Using the cooling system 400, fluid may be drawn in through passive vent 412 (in the suction arrangement) and driven through active vent 422 and orifices 432 (in the expulsion arrangement). Thus, the fluid may efficiently dissipate heat from heat-generating structure 402 in a manner analogous to the fluid driven by cooling system 100. Thus, performance of a device utilizing cooling system 400 may be improved. Further, cooling system 400 may be a MEMS device. Thus, cooling system 400 may small-having a total height not exceeding five hundred micrometers. Consequently, cooling systems 400 may be suitable for use in mobile devices, such as smart phones, other mobile phones, virtual reality headsets, tablets, two-in-one computers, wearables and handheld games, in which limited space is available. Active cooling system 400 may also be used in other compute devices. Because piezoelectric cooling element(s) 410 and/or 420 may be vibrated at ultrasonic frequencies, users may not hear any noise associated with actuation of cooling elements. If driven at or near resonance frequency for the first and second piezoelectric cooling element(s), the power used in operating cooling systems may be significantly reduced.

FIGS. 5A-5E depict an embodiment of active cooling system 500 including multiple cooling cells configured as a tile, or array. FIG. 5A depicts a top view, while FIGS. 5B-5E depict side views. FIGS. 5A-5E are not to scale. Cooling system 500 includes four cooling cells 501A, 501B, 501C and 501D (collectively or generically 501), which are analogous to one or more of cooling systems described herein. More specifically, cooling cells 501 are analogous to cooling system 100. In some embodiments, cooling cell(s) 501 may be analogous to cooling system 400 and/or another cooling system. Although four cooling cells 501 in a 2×2 configuration are shown, in some embodiments another number and/or another configuration of cooling cells 501 might be employed. In the embodiment shown, cooling cells 501 include shared top plate 510 having apertures 512, cooling elements 520, shared orifice plate 530 including orifices 532, top chambers 540, bottom chambers 550 and anchors (support structures) 560 that are analogous to top plate 110 having apertures 112, cooling element 120, orifice plate 130 having orifices 132, top chamber 140, bottom chamber 150 and anchor 160. In some embodiments, cooling cells 501 may be fabricated together and separated, for example by cutting through top plate 510 and orifice plate 530. Cooling elements 520 are driven out-of-phase (i.e. in a manner analogous to a seesaw). Further, as can be seen in FIGS. 5B-5C and FIGS. 5D-5E cooling element 520 in one cell is driven out-of-phase with cooling element(s) 520 in adjacent cell(s). In FIGS. 5B-5C, cooling elements 520 in a row are driven out-of-phase. Thus, cooling element 520 in cell 501A is out-of-phase with cooling element 520 in cell 501B. Similarly, cooling element 520 in cell 501C is out-of-phase with cooling element 520 in cell 501D. In FIGS. 5D-5E, cooling elements 520 in a column are driven out-of-phase. Thus, cooling element 520 in cell 501A is out-of-phase with cooling element 520 in cell 501C. Similarly, cooling element 520 in cell 501B is out-of-phase with cooling element 520 in cell 501D. By driving cooling elements 520 out-of-phase, vibrations in cooling system 500 may be reduced.

Cooling cells 501 of cooling system 500 function in an analogous manner to cooling system(s) 100, 400, and/or an analogous cooling system. Consequently, the benefits described herein may be shared by cooling system 500. Because cooling elements in nearby cells are driven out-of-phase, vibrations in cooling system 500 may be reduced. Because multiple cooling cells 501 are used, cooling system 500 may enjoy enhanced cooling capabilities. Further, multiples of individual cooling cells 501 and/or cooling system 500 may be combined in various fashions to obtain the desired footprint of cooling cells.

FIGS. 6A-6C depict active cooling systems 600A, 600B and 600C used in closed device 610. Thus, the fluid (e.g. air) remains within the device. Referring to FIG. 6A, closed device 610 may be a mobile device such as a smartphones, tablet computer, notebook, virtual reality device, and/or other computing device. Cooling system 600A includes one or more cooling cell(s) 601 and exhaust system 680. Cooling cell(s) 601 are analogous to cooling cells 501, cooling systems 100 and/or 400 and their components described herein. Thus, cooling cells 601 may include cooling element(s) driven to undergo vibrational motion for example at the structural and/or acoustic resonant frequency of the chamber(s) therein, an orifice plate and other structures. However, for clarity, some such structures are not shown. Cooling cell(s) 601 also drive fluid at the speeds described herein using the vibrational motion. Further, cooling cells 601 and, in some embodiments, active cooling systems 600A, 600B, and/or 600C have a low profile. For example, the total thickness of cooling cells 601 and/or active cooling systems 600A, 600B, and/or 600C may be not exceed three millimeters. In some embodiments, the total thickness of cooling cells 601 and/or active cooling systems 600A, 600B, and/or 600C may not exceed than two millimeters.

Heat-generating structure 602 may be an integrated circuit or other structure residing on substrate 670. Heat-generating structure 602 is a source of heat and may be analogous to heat-generating structure 102 and/or 402. Although described as a single component, in some embodiments, multiple components may be present in heat-generating structure 602 and cooled by cooling system 600A. For example, heat-generating structure 602 may also include a heat spreader, vapor chamber, and/or other mechanism for spreading and/or reducing heat. Substrate 670 may be a printed circuit board or other structure. Also shown are components 664, 666 and 667 which may be integrated circuits or other components. Mechanisms for mounting components 664, 666 and 667 are not shown. Although not shown, internal and/or external temperature sensors as well as other components might be employed. Cover 604 that encloses device 610 is also shown. Thus, little to no fluid flow between the interior of device 610 and the exterior of device 610 occurs. Cooling system 600A is attached in proximity to heat-generating structure 602. For example, cooling system 600A may be attached to a frame in proximity to heat-generating structure 602. A jet channel between an orifice plate and heat-generating structure 602, corresponding heat spreader and/or other heat-generating structure may be maintained to allow fluid flow. The flow of fluid in FIG. 6A is depicted by unlabeled arrows.

Cooling cell(s) 601 of cooling system 600A operate in a manner analogous to cooling systems described herein. As can be seen by arrows in FIG. 6A, cooler fluid (e.g. air) near cooling system 600A is drawn toward cooling cell(s) 601. Cooling cell(s) 601 drive fluid from the side distal side from heat-generating structure 602 to the side proximal to heat-generating structure 602. Thus, fluid is driven toward heat-generating structure 602. Heat from heat-generating structure 602 is transferred to the fluid. The fluid exits the region near heat-generating structure 602 carrying away heat from heat-generating structure 602.

Exhaust system 680 directs fluid carrying heat from heat-generating structure 602 away from cooling cell(s) 601. In some embodiments, exhaust system 680 includes ducting through which the fluid travels. The ducting may be enclosed (e.g. analogous to a pipe) or may be open (e.g. forming channels). The fluid travels through device 610 via exhaust system 680 to a region of device 610 distal from cooling cell(s) 601. In some embodiments, exhaust system 680 carries fluid to a region sufficiently distant that heat may be transferred to and dissipated by one or more structures along the path of fluid flow. Stated differently, the fluid may follow a path at least partially through exhaust system 680 such that the fluid exiting cooling system 600A passes one or more components within system 610 and reaches a location distal from cooling system 600A before returning to the cooling cell(s) 601. In some embodiments, the fluid passes a sufficient number or configuration of component(s) and/or a sufficient length of exhaust system 680 that at least ninety percent of the heat transferred from heat-generating structure 602 is removed from the fluid. In some embodiments, the fluid passes a sufficient number or configuration of component(s) and/or a sufficient length of exhaust system 680 that at least eighty percent of the heat transferred from heat-generating structure 602 is removed from the fluid. In some embodiments, the fluid passes a sufficient number or configuration of component(s) and/or a sufficient length of exhaust system 680 that at least fifty percent of the heat transferred from heat-generating structure 602 is removed from the fluid at steady state operation of heat-generating structure 602. Other fractions of heat may be removed in some embodiments. In some embodiments, device 610 includes grooves in substrate 670 and/or case 604 and/or other features used direct the fluid flow after exiting exhaust system 680. In some embodiments, the fluid's path may include a heat sink or other mechanism for dissipating heat. For example, cover 604 may be used to dissipate heat. Consequently, heated fluid exiting heat-generating structure 602 does not immediately return to the distal side of cooling cell(s) 601. Stated differently, cooling system 600A does not simply receive heated fluid from heat-generating structure 602 and drive the heated fluid back toward heat-generating structure 602.

Active cooling system 600A may provide the benefits of cooling system(s) 100, 400, and/or 00. Thus, cooling system 600A may more efficiently and quietly cool heat-generating structure 602 at lower power. Thus, performance of heat-generating structure 602 may be improved. Additional cooling systems (not shown) can be employed and/or cooling system 600A can be increased in size, for example by adding more cells, to cool additional portions of the device, such as components 664 and/or 667. Because active cooling system 600A includes exhaust system 680, heated fluid may be better circulated within closed device 610. As a result, heat from heat-generating structure 602 may be spread among various structures that may be better able to dissipate heat. Thus, performance of closed device 610 may be improved.

In addition, active cooling system 600A may also be used to mitigate issues related to hot spots on cover 604 of device 610A. In conventional devices which do not use active cooling system 600A, hotspots typically develop in the back portion of the cover, just above the integrated circuit or heat spreader (corresponding to the portion of cover 604 just above heat-generating structure 602) due to radiation and/or free convection. To reduce the temperatures at these hotspots, conventional devices typically increase the distance between the heat spreader and back cover (e.g. increase the distance between heat-generating structure 602 and cover 604), place holes above the heat spreader/integrated chip area (e.g. place holes in cover 604 above heat-generating structure 602) and try to use a fan system to pull air through these holes, or place conductive tape on the back cover near the heat spreader/integrated circuit (e.g. place conductive tape in the region of cover 604 near heat-generating structure 602) to conduct heat away from the hot spot to conduct the heat away from the hot spot. However, there may be limited ability to increase the distance between the back cover and the heat spreader/integrated circuit in a conventional system. Typically there is a high flow resistance in the region of the heat spreader/integrated circuit. Thus, a fan may have limited ability to generate a sufficient flow in this region to mitigate hot spots. Further, fans may be unable to be used in devices such as smartphones. Similarly, the use of conductive tape provides only a limited ability to spread heat across the cover. In contrast, when active cooling system 600A is turned on, cooler fluid (e.g. air) flowing toward active cooling system 600A can not only be used to cool heat-generating structure 602, but also naturally cools the region of cover 604 near active cooling system 600A. For example, in some embodiments, the region near the inlet of active cooling system 600A may be at least twenty degrees Celsius cooler than in fluid exiting the region near heat-generating structure 602. In some embodiments, the region near the inlet of active cooling system 600A may be at least thirty degrees Celsius cooler than in fluid exiting the region near heat-generating structure 602. In some embodiments, the region near the inlet of active cooling system 600A may be up to thirty-five degrees Celsius cooler than in fluid exiting the region near heat-generating structure 602. Thus, hot spots area on cover 604 may be reduced or eliminated.

FIG. 6B depicts cooling system 600B used in closed device 610. Cooling system 600B includes one or more cooling cell(s) 601, that are analogous to cooling cells 501, cooling systems 100 and/or 400 and their components described herein. Thus, cooling cells 601 may include cooling element(s) driven to undergo vibrational motion for example at the structural and/or acoustic resonant frequency, an orifice plate and other structures. However, for clarity, some such structures are not shown. Cooling system 600B also includes exhaust system 682.

Active cooling system 600B and device 610 are analogous to cooling system 600A and device 610 depicted in FIG. 6A. Thus, heat-generating structure 602, cover 604, substrate 670, and components 664, 666 and 667 of device 610 in FIG. 6B are analogous to heat-generating structure 602, cover 604, substrate 670, and components 664, 666 and 667 of device 610 in FIG. 6A. However, cooling system 600B includes cooling cell(s) 601 and exhaust system 682.

Cooling cell(s) 601 of cooling system 600B operate in an analogous manner to cooling cell(s) 601 of cooling system 600A. However, cooling cell(s) 601 receive cooled fluid from exhaust system 682. Cooler fluid (e.g. air) near cooling system 600A and within exhaust system 682 is drawn toward cooling cell(s) 601. Cooling cell(s) 601 drive fluid from its side distal side from heat-generating structure 602 to the side proximal to heat-generating structure 602. Thus, fluid is driven toward heat-generating structure 602. Heat is transferred to the fluid. The fluid exits the region near heat-generating structure 602 carrying away heat from heat-generating structure 602. The fluid travels through device 610. In some embodiments, the fluid to a region of device 610 sufficiently distant that heat may be transferred to and dissipated by one or more structures along the path of fluid flow. Thus, fluid entering exhaust system 682 is cooler than fluid exiting the region near heat-generating structure 602. Exhaust system 682 provides a path for the cooled fluid to return to cooling cell(s) 601 as well as to dissipate additional heat. In some embodiments, the fluid passes a sufficient number or configuration of components and/or a sufficient length of exhaust system 682 that at least ninety percent of the heat transferred from heat-generating structure 602 is removed from the fluid. In some embodiments, the fluid passes a sufficient number or configuration of components and/or a sufficient length of exhaust system 682 that at least eighty percent of the heat transferred from heat-generating structure 602 is removed from the fluid. In some embodiments, the fluid passes a sufficient number or configuration of components and/or a sufficient length of exhaust system 682 that at least fifty percent of the heat transferred from heat-generating structure 602 is removed from the fluid at steady state operation of heat-generating structure 602. Other amounts of heat may be removed in some embodiments. In some embodiments, device 610 includes grooves in substrate 670 and/or case 604 and/or other features used direct the fluid flow exiting the region near heat-generating structure and returning to exhaust system 682. In some embodiments, the fluid's path may include a heat sink or other mechanism for dissipating heat. For example, cover 604 may be used to dissipate heat. Consequently, heated fluid exiting heat-generating structure 602 does not immediately return to the distal side of cooling cell(s) 601. Stated differently, cooling system 600B does not simply drive heated fluid from heat-generating structure 602 back toward heat-generating structure 602. Instead, cooler fluid received at and directed by exhaust system 682 enters cooling cell(s) and is driven toward heat-generating structure 602.

Active cooling system 600B shares the benefits of active cooling system 600A. Thus, cooling system 600B may more efficiently and quietly cool heat-generating structure 602 at lower power. Thus, performance of heat-generating structure 602 may be improved. Additional cooling systems (not shown) can be employed and/or cooling system 600B can be increased in size, for example by adding more cells, to cool additional portions of the device, such as components 664 and/or 667. Because active cooling system 600B includes exhaust system 682, heated fluid may be better circulated within closed device 610. As a result, heat from heat-generating structure 602 may be spread among various structures that may be better able to dissipate heat. Thus, performance of closed device 610 may be improved.

FIG. 6C depicts cooling system 600C used in closed device 610. Cooling system 600C includes one or more cooling cell(s) 601, that are analogous to cooling cells 501, cooling systems 100 and/or 400 and their components described herein. Thus, cooling cells 601 may include cooling element(s) driven to undergo vibrational motion for example at the structural and/or acoustic resonant frequency, an orifice plate and other structures. However, for clarity, some such structures are not shown. Cooling system 600C also includes exhaust system 680 and exhaust system 682.

Cooling system 600C and device 610 are analogous to cooling systems 600A, 600B and device 610 depicted in FIGS. 6A-6B. Thus, heat-generating structure 602, cover 604, substrate 670, and components 664, 666 and 667 of device 610 in FIG. 6C are analogous to heat-generating structure 602, cover 604, substrate 670, and components 664, 666 and 667 of device 610 in FIGS. 6A-6B.

Cooling cell(s) 601 of cooling system 600C operate in an analogous manner to cooling cell(s) 601 of cooling systems 600A and 600B because cooling system 600C includes exhaust system 680 and 682. Thus, exhaust system 680 directs fluid from heat-generating structure 602 to regions of device 610 distal from cooling cell(s) 601 in a manner analogous to cooling system 600A. Exhaust system 682 returns fluid to cooling cell(s) 601 in a manner analogous to cooling system 600B. In some embodiments, the amount of heat in fluid dissipated in traversing device 610 is analogous to that described above.

Thus, cooling system 600C may more efficiently and quietly cool heat-generating structure 602 at lower power. Performance of heat-generating structure 602 may be improved. Additional cooling systems (not shown) can be employed and/or cooling system 600C can be increased in size, for example by adding more cells, to cool additional portions of the device, such as components 664 and/or 667. Because active cooling system 600C includes exhaust systems 680 and 682, heated fluid may be better circulated within closed device 610. As a result, heat from heat-generating structure 602 may be spread among various structures that may be better able to dissipate heat. Thus, performance of closed device 610 may be improved.

FIGS. 7A-7C depict cooling systems 700A, 700B and 700C used in open device 710. Thus, the fluid (e.g. air) enters, travels through and exits the device. Referring to FIG. 7A, open device 710 may be a mobile device such as a smartphones, tablet computer, notebook, virtual reality device, and/or other computing device. Cooling system 700A includes one or more cooling cell(s) 701, that are analogous to cooling cells 501 and 601, cooling systems 100 and/or 400 and their components described herein. Thus, cooling cells 701 may include cooling element(s) driven to undergo vibrational motion for example at the structural and/or acoustic resonant frequency, an orifice plate and other structures. However, for clarity, some such structures are not shown. Cooling system 700A also includes exhaust system 780.

Device 710 is analogous to device 610. Consequently, analogous structures have similar labels. Device 710 includes heat-generating structure 702 on substrate 770, cover 704, and additional components 764, 766 and 767 that are analogous to heat-generating structure 602, substrate 670, cover 604, and additional components 664, 666, and 667, respectively. Mechanisms for mounting components 764, 766 and 767 are not shown. Although not shown, internal and/or external temperature sensors as well as other components might be employed. Cooling system 700A is attached in proximity to heat-generating structure 702. For example, cooling system 700A may be attached to a frame in proximity to heat-generating structure 702. A channel between an orifice plate and heat-generating structure 702, corresponding heat spreader and/or other heat-generating structure may be maintained to allow fluid flow. The flow of fluid in FIG. 7A is depicted by unlabeled arrows. Device 710 also includes vents 790 and 792 that allow for fluid communication between the interior of device 710 and the external environment. In the embodiment shown, vent 790 operates as inlet 790 and vent 792 operates as outlet 792.

Cooling cell(s) 701 of cooling system 700A operate in a manner analogous to cooling systems described herein. As can be seen by arrows in FIG. 7A, cooler fluid (e.g. air) near cooling system 700A is drawn toward cooling cell(s) 701. In particular, fluid from inlet 790 travels toward cooling cell(s) 701. Cooling cell(s) 701 drive fluid from the side distal side from heat-generating structure 702 to the side proximal to heat-generating structure 702. Thus, fluid is driven toward heat-generating structure 702. Heat is transferred to the fluid. The fluid exits the region near heat-generating structure 702 carrying away heat from heat-generating structure 702. Fluid carrying heat from heat-generating structure 702 is directed by exhaust system 780 away from cooling cell(s) 701.

Exhaust system 780 may be analogous to exhaust system 680. In some embodiments, exhaust system 780 includes ducting through which the fluid travels. The ducting may be enclosed or may be open, forming channels in device 710. The fluid travels through device 710 to outlet 792. Thus, fluid carrying heat from heat-generating structure 702 can be expelled from device 710 and new fluid from the outside environment drawn in through inlet 790 to cool heat-generating structure. Further, because exhaust system 780 directs the fluid to outlet 792 that is distal from cooling cell(s) 701, heat may be transferred to and dissipated by one or more structures along the path. For example, heat may be transferred to cover 704 and/or component(s) 764, 766 and 767. Thus, the fluid may be cooled at least somewhat before exiting device 710.

In some embodiments, the fluid passes a sufficient number or configuration of component(s) and/or a sufficient length of exhaust system 780 that at least ninety percent of the heat transferred from heat-generating structure 702 is removed from the fluid. In some embodiments, the fluid passes a sufficient number or configuration of component(s) and/or a sufficient length of exhaust system 780 that at least eighty percent of the heat transferred from heat-generating structure 702 is removed from the fluid. In some embodiments, the fluid passes a sufficient number or configuration of component(s) and/or a sufficient length of exhaust system 780 that at least fifty percent of the heat transferred from heat-generating structure 702 is removed from the fluid at steady state operation of heat-generating structure 702. Other amounts of heat may be dissipated in other embodiments. In some embodiments, device 710 includes ducting, grooves in substrate 770 and/or case 704 or other features used direct the fluid flow after exiting exhaust system 780. In some embodiments, the fluid's path may include a heat sink or other mechanism for dissipating heat. For example, cover 704 may be used to dissipate heat. Consequently, heat may be efficiently removed from device 710.

Active cooling system may share benefits of active cooling systems 100, 400, 500, 600A, 600B, and/or 600C. Because cool fluid form outside of device 710 can be used to cool heat-generating structure 702, heat management may be improved. Thus, performance of heat-generating structure 702 may be further improved. Additional cooling systems (not shown) can be employed and/or cooling system 700A can be increased in size, for example by adding more cells, to cool additional portions of the device, such as components 764 and/or 767. Further, exhaust system 780 can be used direct fluid to a distant outlet 792. Thus, outlets 792, and other structures in device 710, may be placed where desired. Consequently, configuration of device 710 may be more flexible. In addition, some heat may be transferred to other portions of device 710 before exiting via vent 792. As a result, the fluid exiting device 710 may be cooler than if vent 792 were placed close to heat-generating structure 702. Thus, discomfort or injury to the user due to fluid flowing through outlet 792 may be mitigated or avoided.

FIG. 7B depicts cooling system 700B used in open device 710. Cooling system 700B includes one or more cooling cell(s) 701, that are analogous to cooling cells 501, 601, 701 cooling systems 100 and/or 400 and their components described herein. Thus, cooling cells 701 may include cooling element(s) driven to undergo vibrational motion for example at the structural and/or acoustic resonant frequency, an orifice plate and other structures. However, for clarity, some such structures are not shown. Cooling system 700 also includes exhaust system 782.

Active cooling system 700B and device 710 are analogous to cooling system 700A and device 710 depicted in FIG. 7A. Thus, heat-generating structure 702, cover 704, substrate 770, inlet 790, outlet 792, and components 764, 766 and 767 of device 610 in FIG. 7B are analogous to heat-generating structure 602, cover 604, substrate 670, inlet 790, outlet 792, and components 664, 666 and 667 of device 610 in FIG. 6A.

Cooling cell(s) 701 of active cooling system 700B operate in an analogous manner to cooling cell(s) 701 of active cooling system 700A. However, cooling cell(s) 701 receive fluid from inlet 790 via exhaust system 782. Cooler fluid (e.g. air) near cooling system 700A and within exhaust system 782 is drawn toward cooling cell(s) 701. Cooling cell(s) 701 drive fluid from its side distal side from heat-generating structure 702 to the side proximal to heat-generating structure 702. Thus, fluid is driven toward heat-generating structure 702. Heat is transferred to the fluid. The fluid exits the region near heat-generating structure 702 carrying away heat from heat-generating structure 702. The fluid travels through device 710 to outlet 792. In some embodiments, heat may be transferred to portions of device 710 between heat-generating structure 702 and outlet 792. In some embodiments, device 710 includes grooves in substrate 770 and/or case 704 and/or other features used direct the fluid flow after exiting the region near heat-generating structure 702. In some embodiments, the fluid's path may include a heat sink or other mechanism for dissipating heat. For example, cover 704 may be used to dissipate heat. Consequently, heated fluid exiting device 710 via outlet 792 may be cooler than if outlet 792 were located close to heat-generating structure 702.

Active cooling system 700B may share the benefits of active cooling system 700A. Thus, cooling system 700B may more efficiently and quietly cool heat-generating structure 702 at lower power. Cooling efficacy of active cooling system 700B may be improved through the use of cooler fluid entering device 710 through inlet 790. Thus, performance of heat-generating structure 602 may be improved. Additional cooling systems (not shown) can be employed and/or cooling system 700B can be increased in size, for example by adding more cells, to cool additional portions of the device, such as components 764 and/or 767.

Further, exhaust system 782 can be used direct fluid from inlet 790, which may be cooler than other fluid in the region of active cooling system 710. Thus, cooling of heat-generating structure 702 may be improved. In addition, inlet 790, and other structures in device 710, may be placed where desired. Consequently, configuration of device 710 may be more flexible.

FIG. 7C depicts cooling system 700C used in open device 710. Cooling system 700C includes one or more cooling cell(s) 701, that are analogous to cooling cells 501, 601 and/or 701, cooling systems 100 and/or 400 and their components described herein. Thus, cooling cells 701 may include cooling element(s) driven to undergo vibrational motion for example at the structural and/or acoustic resonant frequency, an orifice plate and other structures. However, for clarity, some such structures are not shown. Cooling system 700C also includes exhaust system 780 and exhaust system 782.

Cooling system 700C and device 710 are analogous to cooling systems 700A, 700B and device 710 depicted in FIGS. 7A and 7B. Thus, heat-generating structure 702, cover 704, substrate 770, and components 764, 766 and 767 of device 710 in FIG. 7C are analogous to heat-generating structure 602, cover 604, substrate 670, and components 664, 666 and 667 of device 610 in FIGS. 7A-7B.

Cooling cell(s) 701 of cooling system 700C operate in an analogous manner to cooling cell(s) 701 of cooling systems 700A and 700B because cooling system 700C includes exhaust systems 780 and 782. Thus, exhaust system 780 directs fluid from heat-generating structure 702 to outlet 792 that may be distal from cooling cell(s) 701 in a manner analogous to cooling system 700A. Exhaust system 782 directs fluid traveling through inlet 790 from outside device 710 to cooling cell(s) 701 in a manner analogous to cooling system 700B. In some embodiments, the amount of heat in fluid dissipated in traversing device 710 is analogous to that described above.

Thus, cooling system 700C may more efficiently and quietly cool heat-generating structure 702 at lower power. Performance of heat-generating structure 702 may be improved. Additional cooling systems (not shown) can be employed and/or cooling system 700C can be increased in size, for example by adding more cells, to cool additional portions of the device, such as components 764 and/or 767. Because active cooling system 700C includes exhaust systems 780 and 782, heated fluid may be better delivered to outlet 792 (as well as structure(s) in the path to outlet 792) and cooler fluid directed from inlet 790. As a result, heat from heat-generating structure 702 may be better managed. Thus, performance of closed device 610 may be improved.

Exhaust systems used in active cooling systems and in conjunction with cooling cells may take on various configurations. FIGS. 8-15 depict some such configurations. However, other configurations may be employed.

FIG. 8 is a plan view of an embodiment of a cooling system 800 usable with a heat-generating structure. For clarity, only certain components are shown and FIG. 8 is not to scale. Cooling system 800 includes cell(s) 801, chimneys 806 and ducts 880. Cooling cell(s) 801 are analogous to the cooling cells 100, 400, 501, 601, and/or 701 described herein and may be used in connection with a semiconductor structure, electronic device, and/or other heat-generating structure. In some embodiments, a single cooling cell might be included, while in other embodiments multiple cells might be included. For simplicity, any apertures or vents for cooling cell(s) 801 are not shown.

Chimneys 806 provide a return path for fluid from near the heat-generating structure being cooled (on the proximal side of cooling element and not shown in FIG. 8) to the distal side of cooling element. In the embodiment shown, there are four chimneys 806 for each cooling cell(s) 801. In another embodiment, a different number of chimneys 806 may be used. Thus, warmed fluid (e.g. air) that was used to carry heat from a heat-generating structure flows from a region proximate to the structure being cooled, through chimneys 806, to the side of cell 801 shown.

Ducting 880 controls the movement of fluid from the chimneys 806. More specifically, ducting 880 carries the heat-carrying fluid from chimneys 806 to another location. Consequently, the fluid carried by chimneys 806 may be prevented from mixing with fluid that enters cell(s) 801 through aperture(s) not shown in FIG. 8). Thus, the fluid that carries heat away from the heat-generating structure may not mix with the fluid entering cell 801 to be used for cooling the heat generating structure. As a result, cell 801 may have improved cooling performance. In addition, ducting 880 may provide additional mechanical stiffness for cell 801. As a result, vibration of the cooling element(s) for cell 801 may be better mechanically isolated from other cooling cells (not shown in FIG. 8). Consequently, the cooling element(s) for cell 801 may be able to be more readily driven at the desired frequency of vibration. Again, performance of cooling cell system 800 may be improved.

FIGS. 9A-9B are a diagram of a portion of cooling system 900 usable with a heat-generating structure. For clarity, only certain components are shown and FIGS. 9A-9B are not to scale. Cooling system 900 includes a cell 901, apertures 904, chimneys 906 and ducts 910. Also shown are orifices 922. Because orifices 922 are typically in an underlying orifice plate, orifices 922 are shown with dashed lines. Cooling cell 901 is analogous to the cooling cells described herein and may be used in connection with a semiconductor structure or device. In other embodiments, multiple cells might be included. In the embodiment shown, two apertures 904 are included. In another embodiment, another number of apertures, such as single aperture, might be used. Apertures 904 may be in a cooling element analogous to vent 412 in cooling element 410 or may be in a top plate analogous to vent 112 in top plate 110. Chimneys 906 provide a return path for fluid from near the structure being cooled (on the proximal side of cooling element and not shown in FIG. 9) to the distal side of cooling element. In the embodiment shown, there are four chimneys 906 for each cooling cell 901. In another embodiment, a different number of chimneys may be used.

FIG. 9B depicts cell 901 with the air flow indicated by lines and unlabeled arrows. Thus, heated fluid (e.g. air) that was used to carry heat away from a heat-generating structure flows through chimneys 906 at the corners of cell 901 (shown by smaller arrows at chimneys 906). Ducting 910 carries the heated fluid from chimneys 906 to another location such that the heated fluid carried by chimneys 906 may not mix with fluid that enters cell 901 through apertures 904 and is to be used for cooling (fluid flow shown by larger arrows). As a result, cell 901 may have improved cooling performance. In addition, ducting 910 may provide additional mechanical stiffness for cell 901. As a result, vibration of the cooling element(s) for cell 901 may be better mechanically isolated from other cooling cells (not shown in FIG. 9). Consequently, the cooling element(s) for cell 901 may be able to be more readily driven at the desired frequency of vibration. Again, performance of cooling cell system 900 may be improved.

FIG. 10 is a diagram depicting a side view of a portion of active cooling system 1000 usable with a heat-generating structure 1002. Active cooling system 1000 includes cooling cell 1001, chimneys 1070 and ducting 1080. In the embodiment shown, cooling cell 1001 includes two cooling elements (top actuator 1010 and bottom actuator 1020 analogous to cooling elements 410 and 420, respectively), orifice plate 1030 with orifices 1032 therein, chambers (top chamber and bottom chamber), passive valve (also termed aperture 1012 herein) for the top actuator and active valve between the bottom actuator and orifice plate. In the embodiment shown, heat-generating structure 1002 includes a component 1002A such as an integrated circuit and heat spreader 1002B. Also shown are standoff 1005 that may be used to set the height of the jet channel, ducting 1080 and chimneys 1070 that are part of the exhaust system. Other and/or different components may be included.

Cooling cell 1001 functions in an analogous manner to active cooling system 400. In other embodiments, another cooling cell such as cooling system 100 may be used. Consequently, the sizes and operation of cooling cell 1001 are analogous to that of cooling systems 100 and/or 400. Thus, the fluid driven by cooling cell 1001 can cool the heat spreader and, therefore, the underlying integrated circuit (or other heat generating device). In some embodiments, other cooling cells, such as those described herein, may be used in connection with the chimneys and ducting shown in FIG. 10.

Fluid moves along the surface of the heat spreader 1002B to chimneys 1070. The fluid transports heat from heat spreader 1002B (and thus heat-generating component 1002), cooling heat spreader 1002B and integrated circuit 1002A. Chimneys 1070 carry the heated fluid away from heat spreader 1002B. Ducting 1080 can transport the heated fluid away from vent 1012. Thus, the fluid carrying heat from heat spreader 1002B may not readily mix with fluid drawn through the vent 1012 to cool heat spreader 1002B. Consequently, system 1000 may better cool the integrated circuitry. In addition, ducting 1080 may provide additional mechanical vibration isolation to cooling system 1000. Thus, the top actuator 1010 and bottom actuator 1020 may be more easily driven at the desired frequency or frequencies. Consequently, performance of the system 1000 and the device system 1000 is incorporated into may be improved.

FIG. 11 is a diagram depicting a side view of a portion of an embodiment of active cooling system 1100 usable with heat-generating structure 1102. Active cooling system 1100 includes cooling cell 1101, chimneys 1170 and ducting 1180. Cooling cell 1101 is analogous to cooling system 100. In the embodiment shown, cooling cell 1101 includes cooling element 1120 and top plate 1110 having vent 1112 therein, orifice plate 1130 having orifices therein, that are analogous to cooling element 112, top plate 110, vent 112, orifice plate 130 and orifices 132, respectively. In the embodiment shown, heat-generating structure 1102 includes a component 1102A such as an integrated circuit and heat spreader 1102B. Also shown are standoff 1105 that may be used to set the height of the jet channel, ducting 1180 and chimneys 1170 that are part of the exhaust system. Other and/or different components may be included. Cooling cell 1101 thus functions in an analogous manner to active cooling system 100. In other embodiments, another cooling cell such as cooling system 400 may be used. Consequently, the sizes and operation of cooling cell 1101 are analogous to that of cooling systems 100 and/or 400. Fluid is driven through orifices 1132 of orifice plate 1130. The fluid transports heat from heat spreader 1102B, cooling heat spreader 1102B and integrated circuit 1102A. Thus, the fluid can cool heat spreader 1102B and, therefore, the underlying integrated circuit 1102A (or other heat-generating device). In some embodiments, other cooling cells, such as those described herein, may be used in connection with the chimneys and ducting shown in FIG. 11.

In active cooling system 1100, fluid moves along the surface of heat spreader 1102B to chimneys 1170. The fluid transports heat from heat spreader 1102B, cooling heat spreader 1102B and integrated circuit 1102A. Chimneys 1170 carry the heated fluid away from heat spreader 1102B and to ducting 1180. Ducting 1180 transports the heated fluid along the top surface of cooling system 1100 and to the edge of cooling system 1100. Fluid flows down toward heat spreader 1102B and through aperture 1103. Aperture 1103 may be in heat spreader 1102B or at the edge of heat spreader 1102B. Although fluid is shown as being transported only to one aperture 1103 at one side of cooling cell 1101, in some embodiments, multiple apertures that may be at multiple sides of cooling cell 1101 can be used. Fluid is then transported away, for example toward an air vent or other cooling mechanism. Thus, fluid may exit the region below heat spreader 1102B. This flow of fluid is shown by arrows in FIG. 11. Consequently, system 1100 may better cool the integrated circuitry. In addition, ducting 1180 may provide additional mechanical vibration isolation to cooling system 1100. Thus, the cooling element 1120 may be more easily driven at the desired frequency or frequencies. Consequently, performance of the system 1100 and the device system 1100 is incorporated into may be improved.

FIGS. 12A-12B are diagrams of a portion of an embodiment of active cooling system 1200 usable with a heat generating structure such as the integrated circuit shown. FIG. 12A depicts a plan view of cooling system 1200, while FIG. 12B depicts a side view of a portion of cooling system 1200 include a single cooling cell 1201. Cooling cell 1201 is analogous to cooling system 100. In the embodiment shown, cooling cell 1201 includes cooling element 1220 and top plate 1210 having vent 1212 therein, orifice plate 1230 having orifices 1232 therein, that are analogous to cooling element 112, top plate 110, vent 112, orifice plate 130 and orifices 132, respectively. In the embodiment shown, heat-generating structure 1202 includes a component 1202A such as an integrated circuit and heat spreader 1202B. Also shown are standoff 1205 that may be used to set the height of the jet channel and ducting 1280. Other and/or different components may be included. Cooling cell 1201 thus functions in an analogous manner to active cooling system 100. In other embodiments, another cooling cell such as cooling system 400 may be used. Consequently, the sizes and operation of cooling cell 1201 are analogous to that of cooling systems 100 and/or 400. Thus, the fluid can cool heat spreader 1202B and, therefore, the underlying integrated circuit 1202A (or other heat generating device). In some embodiments, other cooling cells, such as those described herein, may be used in connection with the ducting shown in FIGS. 12A and 12B.

In active cooling system 1200, heated fluid is transported between cells 1201 via ducting 1280 that is between orifice plate 1230 and heat spreader 1202B. In this embodiment, chimneys are omitted. Although shown as including sidewalls, ducting 1280 may simply be additional space to which fluid may flow. Thus, fluid moves along the surface of heat spreader 1202B and between cells 1201. Ducting 1280 transports the heated fluid to the edge of cooling system 1200. Fluid is then transported away, for example toward an air vent or other cooling mechanism. Consequently, system 1200 may better cool the integrated circuitry. In addition, ducting 1280 may provide additional mechanical vibration isolation to cooling system 1200. Thus, actuator 1220 may be more easily driven at the desired frequency or frequencies. Consequently, performance of the system 1200 and the device that active cooling system 1200 is incorporated into may be improved.

FIGS. 13A-13B are diagrams of a portion of an embodiment of active cooling system 1300 usable with a heat generating structure such as the integrated circuit shown. FIG. 13A depicts a particular cell 1301, while FIG. 13B depicts multiple cells 1301. Cooling cell 1301 is analogous to cooling system 100. In the embodiment shown, cooling cell 1301 includes cooling element 1320 and top plate 1310 having vent 1312 therein, orifice plate 1330 having orifices 1332 therein, that are analogous to cooling element 112, top plate 110, vent 112, orifice plate 130 and orifices 132, respectively. In the embodiment shown, heat-generating structure 1302 includes a component 1302A such as an integrated circuit and heat spreader 1302B. Also shown are standoff 1305 that may be used to set the height of the jet channel and ducting 1380. Other and/or different components may be included.

Cooling cell 1301 functions in an analogous manner to active cooling system 100. In other embodiments, another cooling cell such as cooling system 400 may be used. Consequently, the sizes and operation of cooling cell 1301 are analogous to that of cooling systems 100 and/or 400. Fluid is then driven through orifices 1332 of orifice plate 1330. The fluid transports heat from heat spreader 1302B, cooling heat spreader 1302B and integrated circuit 1302A. Thus, the fluid can cool heat spreader 1302B and, therefore, the underlying integrated circuit 1302A (or other heat generating device). In some embodiments, other cooling cells, such as those described herein, may be used in connection with the features shown in FIGS. 13A and 13B.

In active cooling system 1300, fluid moves along the surface of heat spreader 1302B toward the exit path. The fluid transports heat from heat spreader 1302B, cooling heat spreader 1302B and integrated circuit 1302A. The exit path guides the fluid away from cells 1301. Fluid may be transported away, for example toward an air vent or other cooling mechanism. This flow of fluid is shown by arrows in FIGS. 13A-13B. Consequently, system 1300 may better cool the integrated circuitry. Consequently, performance of the system 1300 and the device active cooling system 1300 is incorporated into may be improved.

FIG. 14 is a diagram depicting a side view of a portion of an embodiment of active cooling system 1400 usable with heat-generating structure 1402. Active cooling system 1400 includes cooling cell 1401 and ducting 1480. Cooling cell 1401 is analogous to cooling system 100. In the embodiment shown, cooling cell 1401 includes cooling element 1420 and top plate 1410 having vent 1412 therein, orifice plate 1430 having orifices therein, that are analogous to cooling element 112, top plate 110, vent 112, orifice plate 130 and orifices 132, respectively. In the embodiment shown, heat-generating structure 1402 includes a component 1402A such as an integrated circuit and heat spreader 1402B. Ducting 1480 is part of the exhaust system. Other and/or different components may be included. Cooling cell 1401 thus functions in an analogous manner to active cooling system 100. In other embodiments, another cooling cell such as cooling system 400 may be used. Consequently, the sizes and operation of cooling cell 1401 are analogous to that of cooling systems 100 and/or 400. Fluid is driven through orifices 1432 of orifice plate 1430. The fluid transports heat from heat spreader 1402B, cooling heat spreader 1402B and integrated circuit 1402A. Thus, the fluid can cool heat spreader 1402B and, therefore, the underlying integrated circuit 1402A (or other heat-generating device). In some embodiments, other cooling cells, such as those described herein, may be used in connection with the chimneys and ducting shown in FIG. 14.

In active cooling system 1400, fluid moves along the surface of heat spreader 1402B to ducting 1480. The fluid transports heat from heat spreader 1402B, cooling heat spreader 1402B and integrated circuit 1402A. Ducting 1480 transports the heated fluid along the top surface of heat spreader 1402B and past the edge of cooling system 1400. Fluid flows down toward heat spreader 1402B and through aperture 1403. Aperture 1403 may be in heat spreader 1402B or at the edge of heat spreader 1402B. Although fluid is shown as being transported to apertures 1103 at both sides of cooling cell 1401, in some embodiments, multiple apertures and/or apertures only at a single side of cooling cell 1401 may be used. Fluid is then transported away, for example toward an air vent or other cooling mechanism. Thus, fluid may exit the region below heat spreader 1402B. Further, if multiple cooling cells are used, apertures 1403 may only be located at edge(s) of the array of cooling cells or not between every cell. This flow of fluid is shown by arrows in FIG. 14. Consequently, system 1400 may better cool the integrated circuitry. In addition, ducting 1480 may provide additional mechanical vibration isolation to cooling system 1400. Thus, the cooling element 1420 may be more easily driven at the desired frequency or frequencies. Consequently, performance of the system 1400 and the device system 1400 is incorporated into may be improved.

FIG. 15 is a diagram depicting a side view of a portion of an embodiment of active cooling system 1500 usable with heat-generating structure 1502. Active cooling system 1500 includes cooling cell 1501 and ducting 1580. Cooling cell 1501 is analogous to cooling system 100. In the embodiment shown, cooling cell 1501 includes cooling element 1520 and top plate 1510 having vent 1512 therein, orifice plate 1530 having orifices therein, that are analogous to cooling element 112, top plate 110, vent 112, orifice plate 130 and orifices 132, respectively. In the embodiment shown, heat-generating structure 1502 includes a component 1502A such as an integrated circuit and heat spreader 1502B. Ducting 1580 is part of the exhaust system. Other and/or different components may be included. Cooling cell 1501 thus functions in an analogous manner to active cooling system 100. In other embodiments, another cooling cell such as cooling system 400 may be used. Consequently, the sizes and operation of cooling cell 1501 are analogous to that of cooling systems 100 and/or 400. Fluid is driven through orifices 1532 of orifice plate 1530. The fluid transports heat from heat spreader 1502B, cooling heat spreader 1502B and integrated circuit 1502A. Thus, the fluid can cool heat spreader 1502B and, therefore, the underlying integrated circuit 1502A (or other heat-generating device). In some embodiments, other cooling cells, such as those described herein, may be used in connection with the chimneys and ducting shown in FIG. 15.

In active cooling system 1500, fluid moves along the surface of heat spreader 1502B to ducting 1580. The fluid transports heat from heat spreader 1502B, cooling heat spreader 1502B and integrated circuit 1502A. Ducting 1580 transports the heated fluid along the top surface of heat spreader 1502B, at the edges of cooling system 1500. Fluid is then transported away, for example toward an air vent or other cooling mechanism. This flow of fluid is shown by arrows and indicator that fluid flows out of the plane of the page in ducting 1580. Consequently, system 1500 may better cool the integrated circuitry. In addition, ducting 1580 may provide additional mechanical vibration isolation to cooling system 1500. Thus, the cooling element 1520 may be more easily driven at the desired frequency or frequencies. Consequently, performance of the system 1500 and the device it is used in may be improved.

FIG. 16 is a diagram depicting a perspective view of a portion of an embodiment of active cooling system 1600 usable with heat-generating structure 1602. Portions of structures that are covered are indicated by a dotted line. Active cooling system 1600 includes cooling cells 1601 (of which only one is labeled) and ducting 1680. In the embodiment shown, cooling cells 1601 are arranged in an array 1603. Cooling cells 1601 may be analogous to cooling system(s) 100 and/or 400. Consequently, the sizes and operation of cooling cell 1601 are analogous to that of cooling systems 100 and/or 400. Heat-generating structure 1602 may be a heat spreader. Also shown as part of active cooling system are connector 1640 through which electrical connection may be made to cooling cells 1601 and electronics 1650 used in controlling (e.g. driving cooling elements for) cooling cells 1601.

In active cooling system 1600, heat is transferred from heat-generating structure 1602 to the fluid. The fluid is directed to ducting 1680 at the edges of array 1603. Ducting 1680 carries the heated fluid along the surface of heat-generating structure 1602. The fluid is directed by ducting 1680 to past the edge of heat-generating structure 1602. Fluid is then transported away, for example toward an air vent or other cooling mechanism. Some or all of the fluid may then return to the top of active cooling system 1600 and be reintroduced to cooling cells 1601. Consequently, system 1600 may better cool the heat-generating structure 1602. In addition, ducting 1680 may provide additional mechanical vibration isolation to cooling system 1600. Thus, the cooling elements in cooling cells 1601 may be more easily driven at the desired frequency or frequencies. Consequently, performance of the system 1600 and the device system 1600 is used in may be improved.

FIG. 17 is a diagram depicting a perspective view of a portion of an embodiment of active cooling system 1700 usable with heat-generating structure 1702. Portions of structures that are covered are indicated by a dotted line. Active cooling system 1700 includes cooling cells 1701 (of which only one is labeled) and ducting 1780. In the embodiment shown, cooling cells 1701 are arranged in an array 1703. Cooling cells 1701 may be analogous to cooling system(s) 100 and/or 400. Consequently, the sizes and operation of cooling cell 1701 are analogous to that of cooling systems 100 and/or 400. Heat-generating structure 1702 may be a heat spreader. Also shown as part of active cooling system are connector 1740 through which electrical connection may be made to cooling cells 1701 and electronics 1750 used in controlling (e.g. driving cooling elements for) cooling cells 1701.

In active cooling system 1700, heat is transferred from heat-generating structure 1702 to the fluid. The fluid is directed to ducting 1780 at the edges of array 1703 and/or between the rows and columns of cells. For example, additional ducting (not shown in FIG. 17 for clarity) may carry fluid from between the rows and columns of array 1703 to the edges where ducting 1780 resides. Ducting 1780 carries the heated fluid along the surface of heat-generating structure 1702. Fluid may be transported away, for example toward an air vent or other cooling mechanism. Some or all of the fluid may return to the top of active cooling system 1700 and be reintroduced to cooling cells 1701. Consequently, system 1700 may better cool the heat-generating structure 1702. In addition, ducting 1780 may provide additional mechanical vibration isolation to cooling system 1700. Thus, the cooling elements in cooling cells 1701 may be more easily driven at the desired frequency or frequencies. Consequently, performance of the system 1700 and the device system 1700 is used in may be improved.

FIG. 18 is a flow chart depicting an exemplary embodiment of method 1800 for operating a cooling system. Method 1800 may include steps that are not depicted for simplicity. Method 1800 is described in the context of active cooling systems 100, 600C and 700C. However, method 1800 may be used with other cooling systems including but not limited to systems and cells described herein.

One or more of the cooling element(s) in a cooling system is actuated to vibrate, at 1802. At 1802, an electrical signal having the desired frequency is used to drive the cooling element(s). In some embodiments, the cooling elements are driven at or near structural and/or acoustic resonant frequencies at 1802. The driving frequency may be 15 kHz or higher. If multiple cooling elements are driven at 1802, the cooling elements may be driven out-of-phase. In some embodiments, the cooling elements are driven substantially at one hundred and eighty degrees out of phase. Further, in some embodiments, individual cooling elements are driven out-of-phase. For example, different portions of a cooling element may be driven to vibrate in opposite directions (i.e. analogous to a seesaw). In some embodiments, individual cooling elements may be driven in-phase (i.e. analogous to a butterfly). In addition, the drive signal may be provided to the anchor(s), the cooling element(s), or both the anchor(s) and the cooling element(s). Further, the anchor may be driven to bend and/or translate. Also at 1802, feedback from the cooling element(s) is used to adjust the driving current. In some embodiments, the adjustment is used to maintain the frequency at or near the acoustic and/or structural resonant frequency/frequencies of the cooling element(s) and/or cooling system. Resonant frequency of a particular cooling element may drift, for example due to changes in temperature. Adjustments made at 1102 allow the drift in resonant frequency to be accounted for.

Exhaust system(s) are used to direct fluid from and/or to the cooling system, at 1804. The exhaust system may carry heated fluid from the heat-generating structure to an outlet and/or location distal from the cooling cell(s). Similarly, the exhaust system may carry cooler fluid from an inlet or location with the device to the cooling cells.

For example, a cooling element, such as cooling element 120, in one or more of cooling cells 601 and/or 701 may be driven at its structural resonant frequency/frequencies, at 1802. This resonant frequency may also be at or near the acoustic resonant frequency for the top chamber (e.g. top chamber 140). This may be achieved by driving piezoelectric layer(s) in anchor 160 (not shown in FIGS. 1A-1F) and/or piezoelectric layer(s) in cooling element 120. Further, 1802 may be performed for all of cooling cells 601 and/or 701 or some of cooling cells 601 and/or 701. Multiple cooling cells 601 and/or 701 may be driven in-phase or out-of-phase at 1802. In addition, 1802 may be performed in response to various conditions being fulfilled. For example, a surface temperature of a structure reaching or exceeding a threshold, an input from a component device 610 or 710, an input from a user, and/or another condition being fulfilled may result in cooling element(s) of cooling cell(s) 601 and/or 701 being energized.

Also at 1802, feedback is used to maintain the cooling element of cooling cell(s) 601 and/or 701 at resonance. In some embodiments in which multiple cooling elements are driven, the cooling elements phase is also maintained at 1802. For example, cooling elements may be driven and maintained at one hundred and eighty degrees out-of-phase. Thus, the efficiency of cooling elements in driving fluid flow through cooling systems 600C and/or 700C and onto the surface of heat-generating structure 602 and/or 702 may be maintained.

At 1804, exhaust systems 680 and/or 780 are used to direct heated fluid away from heat-generating structure 602 and/or 702. Exhaust systems 680 and/or 780 are also used to direct heated fluid away from cooling cells 601 and/or 70. Similarly, exhaust systems 682 and/or 7802 are used to direct cooler fluid toward the entrance to cooling cells 601 and/or 701. Thus, active cooling systems may more efficiently and quietly cool heat-generating devices at lower power.

Thus, various embodiments of cooling systems, their components, exhaust systems, ducting and method of operations have been disclosed. Various features may be omitted and/or combined in ways not explicitly disclosed herein. As a result, cooling of heat-generating structures may be improved.

Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive. 

What is claimed is:
 1. A cooling system, comprising: at least one heat-generating structure; and a cooling system including a cooling element in communication with a fluid, the cooling element being configured to direct the fluid toward the at least one heat-generating structure using vibrational motion to extract heat from the heat-generating structure; and an exhaust system configured to at least one of direct fluid away from the heat-generating structure to extract the heat and to draw the fluid toward the cooling element.
 2. The system of claim 1, further comprising: an inlet vent; and an outlet vent, the cooling system being configured to draw the fluid from the inlet vent toward the cooling element, and the exhaust system configured to direct the fluid from the at is least one heat-generating structure toward the outlet vent.
 3. The system of claim 2, wherein the exhaust system is configured to direct the fluid in a path past a plurality of components to the outlet vent.
 4. The system of claim 2, wherein the cooling system further includes: at least one of an inlet subsystem and an outlet subsystem, the inlet subsystem including an inlet cooling element in communication with the fluid, the inlet cooling element being configured to draw the fluid from the inlet vent using a first vibrational motion, the outlet subsystem including an outlet cooling element in communication with the fluid, the outlet cooling element being configured to drive the fluid toward the outlet vent using a second vibrational motion.
 5. The system of claim 1, wherein the cooling element has a first side distal from the at least one heat-generating structure and a second side proximal to the heat-generating structure, wherein the exhaust system further includes: a plurality of chimneys configured to direct the fluid from the at least one heat-generating structure toward the first side of the cooling element; and ducting fluidically coupled with the plurality of chimneys and configured to direct the fluid from the plurality of chimneys to a location distal from the first side of the cooling element.
 6. The system of claim 5, wherein the ducting is further configured to direct the fluid in a direction toward the heat-generating structure.
 7. The system of claim 6, wherein the at least one heat-generating structure includes a heat spreader having an aperture therein, and wherein the ducting is configured to direct the fluid through the aperture.
 8. The system of claim 1, wherein the exhaust system further includes: ducting configured to direct the fluid away from the at least one heat-generating structure.
 9. The system of claim 1, wherein the system is incorporated into a mobile device.
 10. The system of claim 1, wherein the cooling system has a total thickness of not more than three millimeters.
 11. A system for cooling at least one heat-generating structure, comprising: a plurality of cooling cells, each of the plurality of cooling cells including a cooling element in communication with a fluid, the cooling element being configured to use vibrational motion to direct the fluid toward the at least one heat-generating structure to extract heat from the heat-generating structure; and an exhaust system configured to at least one of direct fluid away from the heat-generating structure to extract the heat and draw the fluid toward the plurality of cooling cells.
 12. The system of claim 11, further comprising: an inlet vent; and an outlet vent, the system being configured to draw the fluid from the inlet vent toward the plurality of cooling cells, and the exhaust system configured to at least one of direct the fluid from the at least one heat-generating structure to the outlet vent.
 13. The system of claim 12, further comprising: at least one of an inlet subsystem and an outlet subsystem, the inlet subsystem including an inlet cooling element in communication with the fluid, the inlet cooling element being configured to draw the fluid from the inlet vent using a first vibrational motion, the outlet subsystem including an outlet cooling element in communication with the fluid, the outlet cooling element being configured to drive the fluid toward the outlet vent using a second vibrational motion.
 14. The system of claim 11, wherein the cooling element has a first side distal from the at least one heat-generating structure and a second side proximal to the heat-generating structure, the exhaust system further comprising: a plurality of chimneys configured to direct the fluid from the at least one heat-generating structure toward the first side of the cooling element; and ducting fluidically coupled with the plurality of chimneys and configured to direct the fluid from the plurality of chimneys to a location distal from the first side of the cooling element.
 15. The system of claim 14, wherein the at least one heat-generating structure includes a heat spreader having an aperture therein, and wherein the ducting is configured to direct the fluid through the aperture.
 16. The system of claim 11, wherein the exhaust system further includes: ducting configured to direct the fluid away from the at least one heat-generating structure.
 17. The system of claim 11, wherein the plurality of cooling cells has a total thickness of not more than three millimeters.
 18. A method, comprising: driving a cooling element to induce vibrational motion at a frequency, the cooling element being in communication with a fluid and configured to direct the fluid toward at least one heat-generating structure using the vibrational motion; and at least one of using an exhaust system to direct fluid away from the at least one heat-generating structure using to extract heat and drawing the fluid toward the cooling element.
 19. The method of claim 18, wherein the using further includes: directing the fluid from the at least one heat-generating structure past a plurality of components to an outlet vent.
 20. The method of claim 18, wherein the drawing further includes: drawing the fluid from an inlet vent toward the cooling element. 